What causes the Q 's idle to fluctuate up and down?

[SUB ZERO CAR FANATIC]

I think i finally got my transmission issue resolved! still fine tunning, so far so good. After the engine warmed up and thermostat opened engine came up to temp stays just right, anyway i get back after driving around the blocka couple times pull in put it in park and the idles goes up and down, up and down, and its already warmed up, it doesnt do it until its warmed up.

[Haitian_King]

I think i finally got my transmission issue resolved! still fine tunning, so far so good. After the engine warmed up and thermostat opened engine came up to temp stays just right, anyway i get back after driving around the blocka couple times pull in put it in park and the idles goes up and down, up and down, and its already warmed up, it doesnt do it until its warmed up.

MAF? Connectors on it maybe?

I think there's a way to adjust the idle speed, but IIRC you REALLY need to know what you're doing before your touch it.

[maxnix]

IAC valve operating properly? Try 2.5 turns out from closed. Don't rely on engine tachometer for true reading.

[qship96]

What was causing the issues with the transmission?

[SUB ZERO CAR FANATIC]

What was causing the issues with the transmission?

The trans mission lines were backwards like i suspected, glenn...by the way if you read this post, the output line was on the passenger sidenot the driver-side of the transmission. And another thing, i didnt have toomuch transmission fluid it was still too low , i tried running it for 15 minutes orso and checking level is was way more than 1/2 shy, more like 2 1/2 shy.The reason i think it was boiling out was because the fluid was getting way too hot because it was so low , so i just went ahead and added it alland took a chance,after i added the 2 1/2 quarts it quit boiling over whenthe car was not running. Before i couldnt check it after it wasnt runningit was flowing over cause it was too hot,doesnt do it since i added the rest.now i got to figure out the brakes and the idle most importantly. i appreciate everybodys input and suggestions, thanks

[Haitian_King]

IAC valve operating properly? Try 2.5 turns out from closed. Don't rely on engine tachometer for true reading.

That's the valve I thought it was but I didn't want to say it and be wrong. When I posted, I was getting ready to close up the store and didn't have the time to search for it.

[Q45tech]

The ecu has 650 rpm stored as the desired idle speed [when the coolant temp is 174F] however it has the smarts to adjust the desired for stabilty.

The IAC is designed for 15% electronic addition air flow above the manual screw setting.

To maintain idle the ecu can adjust electronic duty cycle and change ignition advance as necessary. I'm sure the software has a feedback loop that decides that X amount of EXTRA Duty cycle should create Y amount of rpm change if not it adds or subtracts 1 degree of advance to find this spot where linearity exists. I has a long term and short term memory that it tries first then corrects,

This searching of just the right combination of duty cycle and advance to create 650 rpm goes on constantly.

When you slow down the ecu only knows you want idle when TPS voltage drops to 0.44 volts [foot off accelerator] then it starts trying what was in memory if it works OK then nothing else happens IF IT DOESN'T then it tries and tries to zero in on the correct combination.

AC on adds complexity because the drag from compressor and extra amps from alternator mean the norma IAC duty cycle is no longer 15% but around 35% so the primary memory is wrong and it has to use short term memory and still search a few tries to get it right.

Look up hysteresis:http://www.lassp.cornell.edu/s....html

Remember the system looks for a stable idle and as engine age the 650 rpm point may not be correct if 1 or more cylinders produces less power than the others. {Always do a power balance test when you spot weird idle to rule out plugs or dirty injectors}, if too much variation check each cylinder for compression variations.

The system was designed for a newish 100% functioning engine so you cannot fix idle rpm variations by tweaking IAC.

The rpms are the mathematical sum of 8 cylinders pushing and dragging the crankshaft around.

[maxnix]

The trans mission lines were backwards like i suspected, glenn...by the way if you read this post, the output line was on the passenger sidenot the driver-side of the transmission.

I thought that was made clear in the first transmission thread you posted.

Hope your plaentary gears aren't fried and clutches aren't scorched from lack of fluid!

[Haitian_King]

The ecu has 650 rpm stored as the desired idle speed [when the coolant temp is 174F] however it has the smarts to adjust the desired for stabilty.

The IAC is designed for 15% electronic addition air flow above the manual screw setting.

To maintain idle the ecu can adjust electronic duty cycle and change ignition advance as necessary. I'm sure the software has a feedback loop that decides that X amount of EXTRA Duty cycle should create Y amount of rpm change if not it adds or subtracts 1 degree of advance to find this spot where linearity exists. I has a long term and short term memory that it tries first then corrects,

This searching of just the right combination of duty cycle and advance to create 650 rpm goes on constantly.

When you slow down the ecu only knows you want idle when TPS voltage drops to 0.44 volts [foot off accelerator] then it starts trying what was in memory if it works OK then nothing else happens IF IT DOESN'T then it tries and tries to zero in on the correct combination.

AC on adds complexity because the drag from compressor and extra amps from alternator mean the norma IAC duty cycle is no longer 15% but around 35% so the primary memory is wrong and it has to use short term memory and still search a few tries to get it right.

Look up hysteresis:http://www.lassp.cornell.edu/s....html

Remember the system looks for a stable idle and as engine age the 650 rpm point may not be correct if 1 or more cylinders produces less power than the others. {Always do a power balance test when you spot weird idle to rule out plugs or dirty injectors}, if too much variation check each cylinder for compression variations.

The system was designed for a newish 100% functioning engine so you cannot fix idle rpm variations by tweaking IAC.

The rpms are the mathematical sum of 8 cylinders pushing and dragging the crankshaft around.

Very informative. So tweaking the IAC isn't a good idea?

[Q45tech]

The problem with the IAC electronic duty cycle is 15% say 150 milliseconds of extra air per second is how much air actually flows. Certainly there is a difference between flows in a clean and dirty IAC.

SO 15% IAC duty cycle is relative, just an open time nothing more!

The ecu monitors MAF to gauge total inflow* and partitions this in its mind [memories] between under closed throttle, manual IAC bypass, and electronic duty cycle air.

* At idle the total air flow will be less than 10 grams [7-8 gm/sec] per second.

Don't be confuse that WOT redline flows ~~ 250 gm/sec not 80 as you would expect from above. Remember the closed throttle plate/ IAC seriously restricts flow by dropping plenum pressure. That's its purpose to choke the engine down so it cannot accelerate [increase idle rpm].

How idle is controlled:http://www.patentstorm.us/pate....html

[GseaQ]

Hi Chris,

I'm glad you got it sorted out. I guess I should have taken the trouble to copy the page before. Maybe I was looking at the IN/OUT from the wrong perspective.

Glenn

[SUB ZERO CAR FANATIC]

I thought that was made clear in the first transmission thread you posted.

Hope your plaentary gears aren't fried and clutches aren't scorched from lack of fluid!

no it wasnt cause no one had a straight foward answer,including yourself!!!

[SUB ZERO CAR FANATIC]

The problem with the IAC electronic duty cycle is 15% say 150 milliseconds of extra air per second is how much air actually flows. Certainly there is a difference between flows in a clean and dirty IAC.

SO 15% IAC duty cycle is relative, just an open time nothing more!

The ecu monitors MAF to gauge total inflow* and partitions this in its mind [memories] between under closed throttle, manual IAC bypass, and electronic duty cycle air.

* At idle the total air flow will be less than 10 grams [7-8 gm/sec] per second.

Don't be confuse that WOT redline flows ~~ 250 gm/sec not 80 as you would expect from above. Remember the closed throttle plate/ IAC seriously restricts flow by dropping plenum pressure. That's its purpose to choke the engine down so it cannot accelerate [increase idle rpm].

How idle is controlled:http://www.patentstorm.us/pate....html

So did i screw up by doing what MAXNIX said to do!!The plugs are bran new all the injectors were cleaned and soaked ininjector cleaner,blown through , all ohmed ok but i guess that doesnt meanthey couldnt be dirty though, i just wouldnt think so i soaked and cleaned them good! So what else should i check if plugs and injectors are ruled out! the car set up for about three years and had little less than 1/4 tankof gas left in it i added gas treatment and and heet then put about 4 or 5gallons of fuel in tank,could any of this affect idle? this is the first time engine has ran in 3 years is what im saying basically, so i wouldnt think anything would be dirty or plugged the engine was completely disassembled and cleaned,engine cleaned internally,fuel rails cleaned,injectors etc.!! what should i try next DENNIS?? THANKS FOR YOUR HELP

[qship96]

no it wasnt cause no one had a straight foward answer,including yourself!!!

I gave you a simple 30 second definitive way to check for yourself....if you chose not to take the initiative to confirm flow pattern and wait for other members to guess,whose fault is that? Spoon feeding stops in the highchair

[SUB ZERO CAR FANATIC]

I gave you a simple 30 second definitive way to check for yourself....if you chose not to take the initiative to confirm flow pattern and wait for other members to guess,whose fault is that? Spoon feeding stops in the highchair

Who pulled your chain!! If i remember correctly i thanked you for your helpand your advice, all i was simply saying to brian was no one knew whichside was the output and that is a fact!!! i didnt say no one helped me or no one told me of ways to check and see which side was output.i try to be appreciative and respectful to everyone here especially myelders who have more experience than me, so why do you have to smart off and be a smart ***, you must be related to maxnix, ask a questionand instead of help or direction you get some immature smart *** response!!nico is a great place and i love it, but all it takes is a couple bad eggs to spoil a good thing!! i dont like to be disrespectful but its hard to respectsomeone who has no respect for others and always flying off at the mouth.if you dont have something helpful and posotive to say like Q45 tech andseveral others on here then keep your rude comments to your self!!!thanks for your wonderful input

[maxnix]

The problem with the IAC electronic duty cycle is 15% say 150 milliseconds of extra air per second is how much air actually flows. Certainly there is a difference between flows in a clean and dirty IAC.

SO 15% IAC duty cycle is relative, just an open time nothing more!

Duty cycle is a pretty good clue as to the condition of the IAC and the intake path in general.

[SUB ZERO CAR FANATIC]

Duty cycle is a pretty good clue as to the condition of the IAC and the intake path in general.

Duty cycle is a pretty good clue as to the condition of the IAC and the intake path in general.

brian........ do i crank car let it warm upshut it down and re-crank , then adjust 2 1/2 turns out? I also cleanedinsides of intake manifold very well. what else could effect idle?what about fuel leak? probably not hugh! i got a fuel leak now, its one ofthe short rubber lines at the back of engine under intake manifold, itsabout 3- 5 inches long from what i can tell and looks like it goes to thesmall little inline fuel filter or valve or whatever it is at thr back and beneathof manifold by rear of passengers side head. is there a special tool or phillips you use to get to those back little fuel lines or do you have to takewhole intake assembly off just to tighten one little fuel line?? thanks

[T45]

If your fuel lines are leaking then you probably have leaking vacuum lines causing your idle fluctuation. Possibly a disconnected line from your transmission venture? If you haven't done a hose rehab now is the time to do it and get it over with. My 92 had not one good hose under the plenum.

[tmorgan4]

Mine does this too. It seems to have a mind of it's own when it comes to the idle.

[GseaQ]

If your fuel lines are leaking then you probably have leaking vacuum lines causing your idle fluctuation. Possibly a disconnected line from your transmission venture? If you haven't done a hose rehab now is the time to do it and get it over with. My 92 had not one good hose under the plenum.

Hi Chris,

Did you hear a whistle while you were unplugging the IAC valve? I did and found the vacuum hose to the Fuel Pressure Regulator was cracked and leaking. All the vacuum hoses are hard for sure. Vacuum leaks will screw up the idle.

Same with the fuel hoses - hard. The hose on the rear passenger side of the rail goes to , I believe (memory fails more every day), the fuel pressure damper. You need a right angle screwdriver and tiny hands to get to it. The screwdriver should be available at a good parts store. I've been through this, though. The clamps will not stay tight on the hard hoses. If you can access them, you can retighten them every month or so until you have the plenum off again and replace them then with the hoses. You'll also find the hose from the left rail to the FPR and the one joining the 2 sides of the rail at the front of the engine will need to be replaced. The front one on our '92 leaked in cold weather for quite a while before I found it.

Glenn

[WesQ]

My idle rmp started to fluctuate this morning also. On start up the rpm drops to about 500, then is over corrected to about 800; then the cycle repeats. However, as I drove her around town for the next 50 minutes it never happended again - solid 650 rpm idle and smooth acceleration. Just on start up in Park. Came out of the store after 2 hours, and the idle fluctuated again on start up, but went away and was a solid 650 rpm as I drove her around town. Cleaned the MAF several days ago, new injectors 3000 miles ago, on my second tank of 44K. I will see if it does it tomorrow. Perhaps a hose connection that leaks when cold and seals after a few minute when it get warm. Is there a difference in how the ecu control idle between Park and Drive?

[GseaQ]

Hi WesQ,

When the IAC valve is clean & adjusted correctly and the throttle body & intake runners/plenum are clean the IAC valve will maintain a pretty steady idle whether under load or not.

I get what's known as a throttle body service done every year. It's the cleaning of the throttle body and plenum/runners with BG chemical "fogger". The idle increased and smoothed out noticeably the first few times it was done. After that the difference was not noticeable - I guess because the regular maintenance I did kept everything cleaner for longer.

Give it a shot before doing anything else. If that doesn't improve the idle significantly, take off the IAC valve and clean it.

Glenn

[maxnix]

brian........ do i crank car let it warm upshut it down and re-crank , then adjust 2 1/2 turns out?

No, just do it at operating temperature.

Might be time to measeure your fuel pressure just to verify proper fuel pump operation. Did Deatsch flush your rails and injectors?
Modified by maxnix at 3:30 PM 3/21/2008

[WesQ]

Thanks Glenn. I will call Jerry Tucker's tomorrow and ask about a 'fogger' treatment.

[SUB ZERO CAR FANATIC]

Whats up Glenn? How ya been doing? yeah your correct i couldnt think at the moment,but the line i have leaking is going to the fuel pressure regulator or the fuel dampner, not sure which it is, its the one closestto pass. side of car.i think its the regulator hose. you know Brian.....i cleaned everything very well when motor was out and dis-assembledand i cleaned the iac valve and all rubber hoses under the plenumand surprisingly they all seem to be in good shape to me , none of them seemed hard or cracked! i had some gas in tank that was in there for about 3 years when car sat, i wonder if that could effect anything if not treated! i put heet and a fuel stabilizer in the tank, i havent filled it up with high octane yet i put about 5 gallons of 90 octane in her, thats about as high as you can get here in Alaska. i dont have plates or registration oranything for car yet so i cant drive but just around block thats why i havent filled her up with gas yet,just adding cans every chance i get to the stationi fill up a couple gas cans of 90 grade, i wish we had 93 octane herelike down in the lower 48! talk to ya later GLENN.

CHRIS

BY THE WAY GLENN I FORGOR TO TELL YOU,I DONT THINK I HAVE A LOOSE OR CRACKEDVACUM LINE, NO WHISTLING AND I WAS VERYTHROUGH WHEN PUTTING ALL RUBBER LINES BACK ON.

[SUB ZERO CAR FANATIC]

No, just do it at operationing temperature.

Might be time to measeure your fuel pressure just to verify proper fuel pump operation. Did Deatsch flush your rials and injectors?

im almost too embarrased to answer that question!! i just soaked them in injector cleaner and cleaned them real good and blew threw them with comp[ressed air. i replaced all the o rings upper and lowerpintle caps and screens and ohmed each one and put them back in.i guess i should send em off to Deatsch Works hugh! maybe ill just buy some new ones payday! i dont think thats my idle issue though,but maybe im wrong. i hear the fuel pump kick on when key is on sounds like its working fine,i need to get a gauge i guess and check fuel pressure.where do you check it at! thanks brian

SUBZERO

[maxnix]

1.) i had some gas in tank that was in there for about 3 years when car sat, i wonder if that could effect anything if not treated!

2.) i put heet and a fuel stabilizer in the tank, i havent filled it.

Condensation and separation are a real problem with fuel that old that has been just sitting. So you have never removed your fuel pump and inspected your tank? You have changed your fuel fiter and plan to do it again soon?

Never Heet! Always ISO Heet! Difference between Methyl and Isopropyl Alcohol. You will need octane booster and a few cans of BG44K as well.

One needs to understand that hoses detiorate from the inside out, especially coolant and fuel and AC hoses. Exterior appearance does not assure interior integrity.

So how's the fuel pressure? Measure with a T fitting after the fuel filter.

[oldmako]

Is is correct that you have 3 year old gas in the car?Even if you added 3-4 gallons to one quarter tank, that's a lousy concentration. It means that over half of the available fuel is junk.

I don't know squat about three quarters of what it discussed on this site, but I do know that if you are concerned about how your car idles while sucking 3 year old gas than you are wasting brow furrows. Get rid of that crap first and get some clean fuel before you chase gremlins which my be caused by the old gas itself. Then you can go after the problems left behind by the junk gas. I find it hard to believe that it runs at all with 3 year old gas.

IF the car runs I'd jam some BG44 into the fresh tank and drive it gently until you can give it the Italian tune up. (WOT down a long straight road)

Because I have a boat, I have to deal with the old / bad gas phenomenon every spring. If my old 60's era Ford 351 (with a Holley carb) runs lousy on old gas God only knows what a FI Q motor would run like.

I read a fairly recent article where they stated that the new E10 fuels begin to suffer significant degradation as little as 30 days. The octane falls right off the map, and it starts to separate. It sure made a believer our of me. I only buy quality gas now, and I plan on running a can of BG through the fuel system every 5000 miles or so.

If I have misunderstood, please accept my apologies. May I offer you a beer (as I am heading tot he fridge as we speak)?

Good luck.

[SUB ZERO CAR FANATIC]

Condensation and separation are a real problem with fuel that old that has been just sitting. So you have never removed your fuel pump and inspected your tank? You have changed your fuel fiter and plan to do it again soon?

Never Heet! Always ISO Heet! Difference between Methyl and Isopropyl Alcohol. You will need octane booster and a few cans of BG44K as well.

One needs to understand that hoses detiorate from the inside out, especially coolant and fuel and AC hoses. Exterior appearance does not assure interior integrity.

So how's the fuel pressure? Measure with a T fitting after the fuel filter.

Brian.......yes i did install new filter with all the other work done to the car, thanks for the tip on the HEET . so just install a tee after filter,and put a gauge on long end of tee, what type of gauge...anythingspecific?? stupid question but had to ask! thanks

[goody90q45]

Hello Chris. A couple of things come to mind. You say it idles fine until it warms up so I'd agree with a previous poster that there could be a leaky vacuum (emissions) hose. If its happening about 20 minutes after starting the engine that's about the time the EGR system starts kicking in. Get a can of brake parts cleaner and spray around all the hoses and intakes listening for idle changes. The entire system is under a vacuum so any leak should suck in the fluid and change the idle.

I'm having injector issues on my 90Q from the PO using a fuel rail that had been in a salvage yard for an unknown period of time (years?). Even though all of the injectors now ohm good, two are still plugged even after a BG injector flush at a local shop. If your fuel rail was sitting around with fuel in it for any length of time (3 yrs?) you may be having the same problems. Unless you've got a laptop and consult, you're going to have to unplug one coil at a time and look at the RPM drop to narrow it down to a cylinder. I haven't seen any FI injector resistance measurements posted either. Tell us what you've got.

At this point if you own a laptop or have access to one, and plan on keeping your Q (I know you do), a good investment for you might be a consult cable and software for about $130. It would take a lot of the guesswork out of the troubleshooting process. Good luck.