RPMS going hay wire.

[alex61089]

So i posted a few times on here about my RPMS and shifting. Current work to date:

Replaced Fuel pump, Spark Plugs, air filter, TPS. Got transmission checked, nothing wrong.Now for the good stuff.

Car picks up fine, drives smooth. until I reach about 60mph Once i reached that it seems like my car lags then gets a sort of Jolt and jumps up in rpm and moves faster. When im up in high RPMs such as 4,000 and I let go of the gas the RPMs drop to 2,000 then shoots back up to 4,000 without me even stepping back on the gas.

After driving, when i stop at a light my rpms go from about 800 (with foot on brake ) down to almost 400 RPMS then it slowly rises up to 800 again.

So what could it possibly be? I'm leaning towards mass air flow sensor, but could it be anything else?

[J30inthe sun]

After driving, when i stop at a light my rpms go from about 800 (with foot on brake ) down to almost 400 RPMS then it slowly rises up to 800 again.

I am experiencing the exact same problem but my rpms drop so much the car stalls. This problem happens about once a day otherwise the idle is fine. It is in the shop as we speak & when they find the problem i will let you know. 1997 J30.

Current parts replaced/work done that could affect idle in the last 6 months:

New TPSCleaned MAFNew air filterNew timing belt kitCleaned Idle Air Control ValveNew OEM NGK spark plugsNew fuel filter

[alex61089]

yeah mine hasent stalled out yet and im hoping i can solve this before it does. Maybe the MAF sensors just need to be replaced?

[J30inthe sun]

No luck today as they were not able to get to my car.



For some reason I just had to post that as I have never seen it before & don't know why anyone would use it.

Feel free to comment on that Icon

[alex61089]

lol. It's uhh interesting? haha.

[J30inthe sun]

The shop says I need a new Idle Air Control Valve. They will have it on friday & will install it then. There check engine light is not coming on & the ECM does not have any stored codes.

I was reading the FSM, the EC section & found this:

Trouble diagnosis for NON-detectable items

One of the items listed is for diagnosis of the Idle Air Control Valve Regulator & Idle Air Control Valve FICD Soleniod Valve.

I don't know if it is the same diagnostics for the 93 J30 & I don't see the FSM listed for the 93 J30 here but maybe the 94 is the same:

http://www.nicoclub.com/FSM/J30/

Check the EC section.

Maybe someone could chime in if there is a the difference of the 93 & 94.

Oh & BTW I am going to go over the car with the CONSULT as well with a fine tooth comb on Friday.
Modified by J30inthe sun at 6:54 PM 4/8/2009

[alex61089]

so this was affecting your rpms while driving and all too? very interesting. Well let me know how it drives because i'll go straight for that being as my idle is going low it would make most sense. (hopefully) lol

[driverdriver]

Diagnostics for '93 and '94 J models are the same.

[J30inthe sun]

so this was affecting your rpms while driving and all too?

No it was not affecting the rpms while driving.

The IACV is designed to catch & maintain the idle when the RPMs drop when coming to a stop & since the CEL & the ECM is not throwing any codes & the IACV is listed as NON detectable item in the FSM hopefully it will clear up my problem.

[alex61089]

yeah see im still having the problem where my RPMS are jumping, i guess the only way to tell what it is is hook up the consult to my laptop and drive it and see what codes come up. Damn i never been more anxious for the mail to come in my life lol.

[yodawill2000]

Have someone else drive while you watch the laptop screen.Don't want to hear about you wrecking.

[alex61089]

But i dont trust anyone with my baby but me

[J30inthe sun]

Brand new IACV installed from teh Infiniti stealership today. Set TPS voltage at 0.52 volts & IACV idle without TPS connected as per the FSM.

I drove for about 1 hour afterwards consisting of about 8 diffentent stops 2 stops included cold starts (engine sitting long enough to be at ambient air temp) & so far no problems.

As Murphy's Law would have it, after a 5 minute test drive after the IACV was installed, I parked it for about 5 minutes, went to leave from the shop & the battery was DEAD! (another Franklin to feed the kitty).



For those keeping tabs:List of things replaced/fixed last 7 months: (108,000 - 114,000 miles) Full timing belt kit w/ all belts & idlersAll coolant hosesFront springsFront struts w/ upper mount & bootsComplete rack & pinion unit w/ mount bushingsFront outer tie rod endsFront stabilizer bar linksFront tension rod bushingsFront lower control armsRight front ABS sensorABS pump unitABS relayHeadlight relayOEM NGK Spark plugsThrottle position sensorIdle air control valve cleaningTrans filter kit & fluidNew rotors & pads all the way aoundNew tires Rear struts & all rubber pieces & boots (1 1/2 years ago)(3 alignments)New IACVNew battery

Cost to bring to spec:

I have put more $ in than the current Kelly Blue Book Suggested Retail Value of this car rated in excellent retail condition (1997 J30 112,000 miles). http://www.kbb.com/KBB/UsedCar...Ctrue

The way the car runs & drives down the road now? PRICELESS... actually there is a price to pay & it is very high.

Modified by J30inthe sun at 3:14 AM 4/11/2009
Modified by J30inthe sun at 3:27 AM 4/11/2009

[alex61089]

wait.. your supposed to have the voltage at 0.52? mine is at 0.44.. what is the correct voltage?

[alex61089]

Well.. I'm thinking... The TPS on IOS's page is 55.00 and says it has power train control. Now i got my TPS from pepboys (25.00) now maybe ( just maybe now ) my rpms are doing this because I am not using a OEM TPS? This is just a guess though. Let me know what you guys think . I'm thinking of ordering this and giving it a shot, if not im sure i can return it.

[J30inthe sun]

wait.. your supposed to have the voltage at 0.52? mine is at 0.44.. what is the correct voltage?

From Page EC-136 in the FSM for the 1997 J30 it says:

The Voltage when the accelerator pedal fully released is approximately 0.35 - 0.65V.

Check the FSM for the 93 which is the same as the 94 to be sure for yours.


Modified by J30inthe sun at 9:22 PM 4/12/2009

[alex61089]

yeah it said from .40 to .50 but .50 was too hard for my J so i re adjusted it to .45.

I'm guessing my RPM problem is from my MAF sensor. I tested the voltage and the FSM states that the voltage should be .8 when the key is switched to on and should be at least .8 to 1.5 V while the engine is on and fully warmed up.My result? i got .2 with the key switched to on and .6 when the engine was fully warmed up.

So it makes sense to me, a faulty MAF will change the shift points of the transmission, waste gas and reduce power and even cause the engine to stall out. I believe the MAF is telling the ECM that more air is passing through than it actually is and is making my gas mixture too lean, Resulting in loss of power.

So what MAF should i go for? Right now there are used ones on Ebay for about 100.00 or i could get a new one (aftermarket) for about 250.00. Theres no way im gonna pay out 500.00 for the OEM from IOS lol...

Edit: Also, if you have a MAF sensor malfunction, a Check Engine light will not show, because as far as the ECM is concerned, The mixture and air flow is correct ( because thats what the MAF reports )

[driverdriver]

Go to Infinitipartsusa.com

Call the toll free number and ask to speak to Joe.

Tell him your a NICO member.

You will get the part at lower price than your hometown dealer.

[alex61089]

I actually got one from NAPA for 250.00 and it came with a 12 month, 18,000 mile warranty. I won't count my chickens before they hatch but the car seems to be driving a lot better

[alex61089]

The car drives better and it gets better fuel economy but my RPM problem is the same. I believe it is the IAC valve, for the simple fact this valve comes into play when you let your foot of the pedal. When i let the foot off the gas at high speeds my rpm goes down then jumps up. Just a gander.. anyone have any more ideas?

[GerryO]

How high are high speeds and what is the engine idle speed with the transmission in Drive, sitting still with your foot on the brake and the engine fully warmed up?

[alex61089]

The Car seems to drive fine until i reach about 70mph ( im assuming 4th gear )When i let go of the gas (meaning i take my foot off the accelerator ) the RPM drops to about 2,000 then jumps up to 3,000. When the RPM drops you can feel the car stop pulling and when the rpm shoots up you can feel it pull like my foot is on the gas but it's not. So usually when im in drive and my foot is on the brake it sits around 800 RPMS but sometimes when i come to a stop the RPMs drop to about 500 or 400 then it slowly comes back up to around 800 RPM.

Alot of people would think it's the transmission and the transmission light has come on and blinked on 3 seperate occassions but that's about it. I get pretty good acceleration. I'm running out of ideas. I'm down to it being the transmission, The IAC valve, a fuel injector failing or unknown lol..

[J30inthe sun]

There is a self diagnostic mode for the transmission. Hopefully someone else with more knowledge than I can chime in on how to go about that.

I change out my MAF last night with a Cardone remanufactured unit from Autozone for $215 & the idle seems fine now. Hopefully that was it. I never had a problem with the rpms dropping while the car was at speed.

Putting on a brand new IACV did absolutely nothing for my idle problems.

Good luck!

[alex61089]

yeah it's not so much that the RPMs are dropping but the fact that they are jumping up when i let go of the gas. hmm... I tried the self diagnostic for the transmission but it didnt work?

[GerryO]

The Car seems to drive fine until i reach about 70mph ( im assuming 4th gear )When i let go of the gas (meaning i take my foot off the accelerator ) the RPM drops to about 2,000 then jumps up to 3,000. When the RPM drops you can feel the car stop pulling and when the rpm shoots up you can feel it pull like my foot is on the gas but it's not. So usually when im in drive and my foot is on the brake it sits around 800 RPMS but sometimes when i come to a stop the RPMs drop to about 500 or 400 then it slowly comes back up to around 800 RPM.

Alot of people would think it's the transmission and the transmission light has come on and blinked on 3 seperate occassions but that's about it. I get pretty good acceleration. I'm running out of ideas. I'm down to it being the transmission, The IAC valve, a fuel injector failing or unknown lol..

Idle speed is a bit high and can be adjusted down using the screw on the side of the IACV.

A failing injector will trigger a CEL and simply cause the engine to run rough and be under-powered.

Cruising rpms at 70 mph should be about 2,800 and drop when you let off the accelerator and increase to 2,800 or more when you get back on it and how hard you push the pedal.

Sounds almost like the transmission is down-shifting on its' own or the cruise control is at work, and of course the ECM processes all of the various input signals and controls the outputs, so either it's getting an incorrect input, it's bad or an output is getting to where it needs to go. Fortunately my transmission light has never blinked, but when my TPS was out of adjustment (low output voltage) cruising rpms were high, gas mileage suffered and the transmission hunted at freeway speeds (OD lock-up wasn't consistent and down-shifts were too easy/frequent).

It's as if the car doesn't know the proper combination of how fast it is moving, the engine rpms, what gear the transmission is in and the throttle position.

Are similar symptoms listed anywhere in the FSM diagnosis and trouble-shooting section?

[alex61089]

The FSM is very uninformative when it comes to these issues, it just gives you a procedure to check if the part is bad ( with voltmeter ). It's almost as if the transmission is being told ok shift up to pick up speed, oh no wait go back down, no wait shift up uhh sorry.. shift down. I put a new MAF in it, the TPS voltage is set correctly, perhaps it's the TPS itself? i do not believe it is OEM so could that be causing the problem? I know the IAC valve is a pain to get to so i want to make sure it's that before i jump on it. But as J30 thought it was that, it wasent and i cant seem to believe that this valve is causing my Hunting.

[driverdriver]

Transmission self diagnostics instructions are located in this thread:

zer...age=2

[alex61089]

i did that and it doesnt work?

[yodawill2000]

Light never comes on ??Are you doing it EXACTLY as its shown ?

[GerryO]

The FSM is very uninformative when it comes to these issues, it just gives you a procedure to check if the part is bad ( with voltmeter ). It's almost as if the transmission is being told ok shift up to pick up speed, oh no wait go back down, no wait shift up uhh sorry.. shift down. I put a new MAF in it, the TPS voltage is set correctly, perhaps it's the TPS itself? i do not believe it is OEM so could that be causing the problem? I know the IAC valve is a pain to get to so i want to make sure it's that before i jump on it. But as J30 thought it was that, it wasent and i cant seem to believe that this valve is causing my Hunting.

Don't think it's the IACV either, although there is a FIAC (fast idle control valve) too.

Are your throttle bodies clean, properly lubricated with the shaft moving freely/smoothly; and how about the amount of slack/free play in your throttle and Cruise Control cables, and the general condition/cleanliness of your throttle return springs? Are the butterflies properly synchronized?

It would be great to see what the TPS voltage is doing when these things are happening, as the throttle body butterflies may not be closing completely/reliably when you take your foot off of the pedal. The TPS contains a variable resistor that controls the output voltage going to the ECM.