High Idle, part II

[elwesso]

OK im *really* trying to get to the bottom of this, id appreciate any input.. Unfortunately, Robs advice with giving the car some xanax didnt work

First of all there are 2 problems, one the car idles high when fully warm (about 1000 RPM) and also, if you restart the car say 5 mins after it has been shut off the idle goes nuts.. Heres a video

http://www.q45.org/qidle.AVI

So yesterday I decided to go on a quest to figure this damn thing out... now I wont say its absolute because my multimeter could be (is) a POS... I decided to start narrowing things down, so I started messing with the TPS (bad move).. I was gonna try and do the resistance thing, but for some reason i could never get a resistance value.. I put my DVOM at the lowest setting (200) and its open circuit throughout the range.... Then I moved it to the higher setting (like 20k) and it registered but still almost open circuit (like 300 ohms or something)...

No matter how i adjust the TPS it still idles high. I moved it yesterday (marking it first) and i moved it a little, then when i moved it back to its original place, the idle went to like almost 2000 RPM.... So I had to adjust it all the way back to get it to idle where it would before.....

Im thinking that the TPS is possibly progressively getting worse... peformance seems about the same, but im getting about 17-18MPG on the highway (o2 sensors have about 32k on them), which is much lower that it should, and city mileage is unthinkable, but not that much worse than my old Q.. Thats a seperate issue, but it might be related... Torque converter lockup doesnt happen like it should, but that could be related to using a 90 TCU (2nd gera start for winter)... You have to press the gas down in order to get it to lock, its much more pronounced with the level 10 transmission and high stall converter...

I will get the TPS from my old Q and see if that does anything for me..

Any input would be appreciated!

[elwesso]

Wanted to add that I made a booboo that it was in K ohms, and i didnt notice that :

However, when i put it at the OEM setting (700ohms) it was WRONG... Its now at .4 and now im back to where we started...

[Q45tech]

The non Consult method is worthless. The TPS must be set at 0.44 volts as read by Consult. Then the IAC- ADJUSTED TO 2.5-3-3.5 TURNS OUT. while monitoring IAC duty cycle and rpm...........sounds like the coolant temp is not correct [176F] or someone has been messing with TB screws warm up offsets /throttle linkages.

[elwesso]

OK... Will take to NISSAN dealer.. Ill take the coolant temp sensor and TPS off my old Q and we'll give it a try...

i know fred didnt mess with anything TB related, and I didnt either.....

[elwesso]

Alright I swapped out the TPS, even though it really wasnt that big of an issue.....

The weird thing is... I adjusted it to .44volts as read on the AT control unit, pins 34 and 35... I couldnt find a place to read it directly on the ECU, and since the ECU picks its signal up before the TCU, i figured this would be fairly accurate.... At least to get it close..

I adjusted it to .44 volts and it idled crazy..... LIke 1500 or something... Then I pushed it all the way in, and it read like .88 volts and it idles back to where I was...

Next im gonna try the coolant sensor... Ill buy a new one, but I cant find a socket to go on it.. It has to be deeper than normal, but not a true deep socket.....

[Q45tech]

Remember to disconnect the IAC connector that way the base idle can be set without ecu adding air [opening IAC [10-15%]]...........just the IAC screw air bypass and under throttle plate supplying air [what those tiny notches in botom of TB do.

Then ecu adjust injector opening time and ignition advance to maintain 550-600, then IAC [reconnected] adds 10-15% =~~650-700.

Think about how important the IAC balance point is, it must be just right to raise or LOWER idle.

Same with base ignition advance [15 degrees hot with timing light]....the ecu assumes it is absolutely correct as otherwise everything will be offset in real terms.

Have you tried replacing ecu, as I remember Freds was funky [or am I confused with what car you are driving]?

I always look [with Consult] at MAF voltage to make sure it is close for conditions to find air leaks or MAF problems [ 0.1 or 0.2 volts error is about all the ecu can tolerate.

[Jesda]

I, too, am experiencing high idle when the engine is warm or cold (in Park -- everything is normal in Drive). I previously fiddled with the IAC to make driving the Q tolerable prior to injector replacement.

I didnt think to remove the IAC connector before readjusting. Thanks Dennis!

[elwesso]

Remember to disconnect the IAC connector that way the base idle can be set without ecu adding air [opening IAC [10-15%]]...........just the IAC screw air bypass and under throttle plate supplying air [what those tiny notches in botom of TB do.

Then ecu adjust injector opening time and ignition advance to maintain 550-600, then IAC [reconnected] adds 10-15% =~~650-700.

Think about how important the IAC balance point is, it must be just right to raise or LOWER idle.

Same with base ignition advance [15 degrees hot with timing light]....the ecu assumes it is absolutely correct as otherwise everything will be offset in real terms.

Have you tried replacing ecu, as I remember Freds was funky [or am I confused with what car you are driving]?

I always look [with Consult] at MAF voltage to make sure it is close for conditions to find air leaks or MAF problems [ 0.1 or 0.2 volts error is about all the ecu can tolerate.

Thank you Dennis.. The IAC is adjusted IN all the way right now to maintain it... Seems to be no difference.. I also changed IACs with one that should be perfectly clean.....

Right now I have the timing set to about 15 degrees..... I called JWT and they said you have to jump the TPS with the middle one and 5v (not sure why?)... I did that and had the TPS connected as well, and its solidly set at 15 degrees... I check it every now and then, or at least i did for a week or so...

I'll pull out the ECU tonight and swap in my old Q... The reason the ECU is goofy is because it was for a TCS car, and it throws a TCS code since this Q doesnt have TCS... Apparently the Q45t without TCS is pretty uncommon! Im still driving Freds Q..... I did swap ECUs once a long time ago and It didnt make any difference..... I drove on a stock ECU for about 200 miles and nothing changed...

Dennis, what do you think is going on with my TPS.. Right now I have the TPS adjusted all the way counter clockwise.. Its at like .88 volts and it seems to idle fine (as read from the TCU)....

I dont want to take it to the dealer because I doubt they know what their talking about!!!

Next Ill try the coolant sensor, but im not sure thats the problem, but $15 and 10mins to install it makes it worthwhile.....

Edit: I also changed my TPS (as noted earlier) with a known good one and it is exhibiting the same behaviors.....

[Q45tech]

How are you measuring rpm, can't trust the tach at the bottom end of range.........what you think around 700-800 may be 100 rpms off.

The TPS must stay [be set] between 0.4 and 0.5 volts as read by ecu not the VOM method with coolant at 176F [170-185F]..........this is with oem air box/filter not dreaded KN cone or other junk.

What is idle vacuum [hate that word] as measured by teeing to FPR vacuum port ~~18" HG what is MAF voltage............couple of degrees in timing 14-16 is all that is allowed.........sure the throttle cable at TB is loose eough .....1/4" downward pressure before rpm change.

Did someone bypass the coolant lines to TB [hot wax warmup system]?

[PoorManQ45]

Could the IAC be the cause of high idle?

WHat is your timing set to?

TPS improperly reading. Possibly malfunctioning.

*edit* I just read that you changed out the IAC with a different one. Try turning the adjustment on it. What does that do?

[911/Q45]

Next im gonna try the coolant sensor... Ill buy a new one, but I cant find a socket to go on it.. It has to be deeper than normal, but not a true deep socket.....

Lots easier to swap the coolant sensor if you remove the temp gauge sensor first.

[PoorManQ45]

Which sensor? the one behind the filler neck, or the one in the valley?

Either way, a pivoting open end box wrench should work

[elwesso]

There is only one sensor on federal models which thats what my Q is...

Don, thanks ill remember tha.t

PMQ, i already tried all those things!

How are you measuring rpm, can't trust the tach at the bottom end of range.........what you think around 700-800 may be 100 rpms off.

The TPS must stay [be set] between 0.4 and 0.5 volts as read by ecu not the VOM method with coolant at 176F [170-185F]..........this is with oem air box/filter not dreaded KN cone or other junk.

What is idle vacuum [hate that word] as measured by teeing to FPR vacuum port ~~18" HG what is MAF voltage............couple of degrees in timing 14-16 is all that is allowed.........sure the throttle cable at TB is loose eough .....1/4" downward pressure before rpm change.

Did someone bypass the coolant lines to TB [hot wax warmup system]?

Dennis, im starting to think that someone bypassed this or something... Last night as I was piddling with it, i left the IAC unhooked... When I started the car it idled at about 800.. Then when I went to leave school, i started it up and it did the same thing... then i reattached the IAC and it went up to 1200 like its supposed to... Im starting to think something is goofy with the TB...

[PoorManQ45]

Dennis, im starting to think that someone bypassed this or something... Last night as I was piddling with it, i left the IAC unhooked... When I started the car it idled at about 800.. Then when I went to leave school, i started it up and it did the same thing... then i reattached the IAC and it went up to 1200 like its supposed to... Im starting to think something is goofy with the TB...

Hm.. So the car idled fine without the IAC on? Did you try driving it that way?

What would happen if the IAC were completely bypassed? What Exactly does the IAC do?

[elwesso]

No the car idled low at startup and normal at warmup.....

The IAC controlls the idle..... the search function is there!!!

[Q451990]

Can you swap your old TB onto this car, or did one have TCS while the other doesn't?

Heath

[elwesso]

Right and also if you noticed the TB is gone, with the rest of the engine!

[DAEDALUS]

Does the car not have a fast idle cam? I didn't see it mentioned. You can just visually check if the coolant hoses are bypassed on the TB. Keep an eye on the IAC voltage while the idle's fluctuating. Still trying to stress that swapping parts is usually not the way to go about figuring out what's wrong. At least you're not paying dealership retail on the parts, but the labor (your labor) is always there. You can always backprobe voltages at the ECU, even for the TPS.

[Q45tech]

Other than maintaining idle [what the zero to 80% duty cycle does] under various auxillary load changes [AC, PS load, [voltage -alternator demand for HP]...............the IAC acts as a "dashpot",when you suddenly let off throttle at speed to avoid the engine dying with throttle closed.......steps down rpm as speed decreases....CRITICAL function.

Stange how people want to disconnect components when they won't take the time to figure out what's wrong.

"Fast idle cam" is really a hot wax controlled spring/plunger heated by coolant in TB.

[PoorManQ45]

Stange how people want to disconnect components when they won't take the time to figure out what's wrong.

Bah.. Who needs those electronic gismos anyways

Do you know if there is any particular reason for the placement of the IAC? I have the plenum off, and I noticed that a hose goes from the intake, before the TB, to the IAC, and then back to the TB. The hose coming from the IAC appears to come in right after the throttle plate. I don't understand why they put the IAC so far away from the TB. It would seem to me that it'd be easier to put it closer to the TB, possible right on the TB.

[Jesda]

Can the AAC/IAC be sealed with RTV or is the Nissan gasket required?

Thanks!

[Q451990]

I would use the OEM gasket. I'm sure RTV would seal it, but it would be a pain to scrape off, and if you get any overlap squiriting into the passages in the plenum or valve, that could be a problem.

Heath

[PoorManQ45]

and if you get any overlap squiriting into the passages in the plenum or valve, that could be a problem.

Heath

Hm... I'm looking at my plenum right now. And it appears that where the physical IAC sits, it does not enter the plenum. It has a hose coming into it from the intake, and a hose going out of it to near the TB. That''s it.

But I understand what you mean about the RTV being harder to work with. It'd be very tricky to not have any pinch into the passage way

[elwesso]

Does the car not have a fast idle cam? I didn't see it mentioned. You can just visually check if the coolant hoses are bypassed on the TB. Keep an eye on the IAC voltage while the idle's fluctuating. Still trying to stress that swapping parts is usually not the way to go about figuring out what's wrong. At least you're not paying dealership retail on the parts, but the labor (your labor) is always there. You can always backprobe voltages at the ECU, even for the TPS.

I dont care about the labor... It keeps me off of NICO for a few minutes.

I will double check....

Other than maintaining idle [what the zero to 80% duty cycle does] under various auxillary load changes [AC, PS load, [voltage -alternator demand for HP]...............the IAC acts as a "dashpot",when you suddenly let off throttle at speed to avoid the engine dying with throttle closed.......steps down rpm as speed decreases....CRITICAL function.

Stange how people want to disconnect components when they won't take the time to figure out what's wrong.

"Fast idle cam" is really a hot wax controlled spring/plunger heated by coolant in TB.

Actually I forgot to plug it back in... I had it unplugged when I was trying to set, and I went to eat diner... never made it back out to the Q.....

[DAEDALUS]

Labor is only one aspect of course. Certainty is another. If you wanted to keep guessing you wouldn't have started either thread Watch your voltages--they tell you exactly what's going on with the parameters they measure/output to. RPM is DIRECTLY related to air supply. Is the air coming from the IAC via ECU signal? Is it even coming through the MAF or is it a vacuum leak? There is also a procedure for checking your FIC, with a temp chart.

[Q451990]

Hm... I'm looking at my plenum right now. And it appears that where the physical IAC sits, it does not enter the plenum. It has a hose coming into it from the intake, and a hose going out of it to near the TB. That''s it.

But I understand what you mean about the RTV being harder to work with. It'd be very tricky to not have any pinch into the passage way

It has passages that flow directly into the plenum... The hose(s) feed the valve.

Heath

[s13sr20chris]

i dont mess with the q's too much but i have to think this is one of those situations where you just work backwards. the only issue is the idle right? and maybe some fuel consumption issuesso it idles high but with iac is ok.the base idle/ign timing is correct.for some reason the iac is working overtime.not iac as it was checked with known good.i dont have an fsm with me is the q iac a stepper motor or pulse-width activated type?the ecm(or possible harness fault) is commanding extra rpms/air(this assumes its not a vac leak)does the ecm think there is a load(p/s switch, a/c switch, etc.)is the ecm in failsafe for some other component?

sorry for all the questions and going over stuff you guys have already been over. im am just trying to get in on the action.

[elwesso]

i dont mess with the q's too much but i have to think this is one of those situations where you just work backwards. 1. the only issue is the idle right? and maybe some fuel consumption issues2. so it idles high but with iac is ok.3. the base idle/ign timing is correct.4. for some reason the iac is working overtime.5. not iac as it was checked with known good.6. i dont have an fsm with me is the q iac a stepper motor or pulse-width activated type?7. the ecm(or possible harness fault) is commanding extra rpms/air(this assumes its not a vac leak)8. does the ecm think there is a load(p/s switch, a/c switch, etc.)is the ecm in failsafe for some other component?

sorry for all the questions and going over stuff you guys have already been over. im am just trying to get in on the action.

Chris, thanks!!!

1. Yes2. It idles high, wether the IAC is plugged in or not.3. indeed4. I guess, but since its the same when its unplugged i dont know5. Correct6. I think its pulse width.. I would assume since dennis has suggested checking with an osscilloscope7. I swapped in a known good ECU8. LIke I said, same conditions with a known good (and non modded) ECU!

[s13sr20chris]

ah hah, no change when the iac is disconnected! that helps. that makes me think its a)intake leak(with some other associated problem)b)thottle is partially openc)iac not shut all the way(but you swapped it out)d)one of the other myriad of idle valves may be operating(does the q have ficd or aav as a separate valve?)

[elwesso]

It still could be a leak i guess, ill take it to my shop and have them put on the smoke machine....

As far as i know, the only idle devices are hte IAC/AAC valve (all one assy) and the fast idle cam...