Strange Idle Issues *Dies At Lights&

[Rabbi]

Recently brought back a 92 z34 from the dead. The Crank position sensor was replaced.

The car runs great, Pulls hard and sounds perfect.


No vacume leaks that im aware of. The car is not throwing any codes at all since i cleared them.

The car seems to like to die in gear while i stop at lights or at stop signs, This seems to only happen when the cars in drive. Doesnt happen in park at all.

What would be the cause of this?

Thanks

[DnaProRacing]

been thru this myself with same year/model Lq1. you need an upper intake cleaning, tps/iac sensors cleaned, then drain a pint of tranny fluid out, add a pint of seafoam transtune, drive normal for a couple days, then flush the tranny. many people believe the idle/stalling issue to be one of two things, carbon buildup in the upper intake along with carbon buildup on the sensors or tcc lockup in the tranny. try these then post back your results...

[torq455]

don't flush the tranny unless you've had good fluid maintenance, otherwise, with the new fluid and detergents breaking down small dirty areas, that can cause valves to stick. I had the same issue, but more intermittent with my 97 lumina 3100. i cleaned the MAF and that helped quite a bit.

[Rabbi]

interesting, The previous owner added one of those ebay short ram air intake pipes. The hot air intake.


I Dont even think the maf is connected. Wouldnt that throw a code though?

Ill have to check this out after work lol.

[DnaProRacing]

theres no maf on the 92. just map. and no that wont throw codes.

[torq455]

well, if your car isn't supposed to have a MAF it won't throw a code. if you don't have a sensor plugged in, yes, you will get a code saying either no signal or sensor input low voltage.

[RedZMonte]

Recently brought back a 92 z34 from the dead. The Crank position sensor was replaced.

The car runs great, Pulls hard and sounds perfect.


No vacume leaks that im aware of. The car is not throwing any codes at all since i cleared them.

The car seems to like to die in gear while i stop at lights or at stop signs, This seems to only happen when the cars in drive. Doesnt happen in park at all.

What would be the cause of this?

Thanks

What happends when you put the car in neutral when coming to a stop? does it sputter and dye or just idle down and die? when it happends is the hot or cold or does it matter? if you give it throttle does it stay running? hard to say what is going on. it may be benifitial to get someone with a scan tool to scan it while driving. if it only happends in gear then it may like someone said be going to tcc lockup. if it happends when you pop it into neutral then you can safly assume the tcc is not the problem.

S

[Rabbi]

What happends when you put the car in neutral when coming to a stop? does it sputter and dye or just idle down and die? when it happends is the hot or cold or does it matter? if you give it throttle does it stay running? hard to say what is going on. it may be benifitial to get someone with a scan tool to scan it while driving. if it only happends in gear then it may like someone said be going to tcc lockup. if it happends when you pop it into neutral then you can safly assume the tcc is not the problem.

S

it happens in neutral as well i think.

I Did start the car up this morning and it didnt want to stay running, It was cold as balls outside to.

But once it warmed up it ran fine, other than the stall at light problem.

[latemodelnewbee]

my 91 z34 does the same thing when its warm, it just hiccups and dies. i have a voltage meter in the car it drops down to high 12'sV and then dies I thought it was related to that. I redid all the power wires from the battery to starter to alternator with 2 gauge wire, it helped but still does it. the only ses light i get is for the VSS since i have to rev it alittle(1000-1500 rpm) the make sure it won't die but it didn't do that until after i swapped in the five speed, so thats no big deal. I'll have to check the sensors listed.

[RedZMonte]

it happens in neutral as well i think.

I Did start the car up this morning and it didnt want to stay running, It was cold as balls outside to.

But once it warmed up it ran fine, other than the stall at light problem.

the part about it not wanting to run when cold until it got hot sounds like Intake gasket.. intake gasket could case it to stall as well i would think if its leaking enough... it would also not cause a check engine light.... just a thought.

You also said you replaced the crank position sensor... could it be a bad sensor?

S

[Stinky_1]

not sure why the OP never came back and posted what fixed it? Maybe its still broken?

I have a Z34 that I picked up this winter. Its doing basically the same thing. It worked fine while it was really cold outside. But I only drive for 5 minutes at a time. So it never really warmed up. Now that its getting warmer out, the car starts up warmer. Its is very hit and miss with the problem though. For example I went out there 10 minutes ago to start trouble shooting, and it idled just fine. Ran around the block and still worked fine.

What I have done so far is replace the ICM and all 3 coil packs. Still had the problem
Replaced the spark plugs and its still there.

I am not sure if its a fuel delivery problem, or a spark problem, or a sensor problem. I find the carbon buildup theory interesting, I wouldnt have suspected that. If anything, I would suspect the IAC valve is built up with carbon. not the entire intake. But, AT this point I will try anything!

The next steps I planned to take. Once it starts doing it again....

Unplug the egr valve and see what effect that has
Plug my fuel gauge on the port and see what the fuel pressure is doing.
Unplugg a vacuum line and see what happens to idle
Unplug the IAC valve and see what happens.

One thing I do know, is that when its doing it, unplugging any of the spark plug wires makes no specific changes to the idle. Which was why I suspected the ICM was the problem. I figured it was acting up, and not knowing when to spark. This could still be the problem, but, instead of the ignition control module having the problem, it could be the signal its getting is bad. Meaning my Cam angle sensor is acting up??

My current theory is that my fuel pump is the problem. My reason for this thought is a few. First of all, it seemed to originally make the problem the most when the gas tank was low. AFter a fill up it seemed to be fine. Now, it does not matter. I suspect though that it ends up running lean, so the O2 sensor is calling for more fuel, which, it eventually gets when the pump works again. This makes it go over rich and starts to bog down, so it leans out, then the pump starts acting up again making it go too lean, eventually almost stalling. Then we get a vicious cycle.

So, next time it starts acting up, I will have a few things to try and see whats going on. If it was the TPS as suggested above, it would be VERY easy to test. Just throw a multimeter on, turn the ignition to on, and do a sweep reading of the ohms. If it ever jumps to 0, or goes to infinity at any point, then it needs to be replaced. If its smooth and linear, then that is not your problem.

If anyone else has had this problem and has succesfully fixed it, I am all ears as to what did it for you.

[Stinky_1]

so,

I got it to start acting worse recently. I checked the fuel pressure, which was great. I checked for vacuum leaks, when I created my own by pulling hoses off, the idle went up higher, but the stumble was still there. It maybe was not going to stall, but it certainly was not running better.

I think that proves that it is NOT something to do with a bad gasket in the intake system, or carbon buildup. since I would expect different results by creating vacuum leaks.

I am starting to wonder about the idea of draining some tranny fluid, and putting in cleaner. It does make sense..... If there is a sensor in there to tell it when I am shifting, and that sensor gets stuck for whatever reason, then the car would think that its always shifting. I read somewhere that they had to add a throttle cut to the system on shifts because the tranny could not handle the power. So, I imagine it working a lot like how the ignition cutout works on a boat while shifting. Which would also explain the inconsitant spark on all cyl, not just one.

So, Tomorrow I will be giving the tranny flush a go, and see how that works. I have tons of bottles of fluid. So adding some cleaner to the mix wont be a problem.

I will post up how it goes. Maybe I will find the problem before I am sick of the car.

If anyone else has input, I would love to hear it

[86FieroSEv6]

Have you checked that the throttle is clean? Have you checked for minimum idle air rate? I have found more worn and maladjusted throttles than you can throw a wad of beavers at. Also, don't forget to check on a sticking/jammed idle air control valve.

[Stinky_1]

By mal adjusted throttle, your talking the TPS? I didnt look very closely at that.

I wouldnt suspect a sticking IACV simply because pulling a vacuum line off raises the idle up, not drops it. And I wouldnt put much money on it sticking closed, since closed is where I want it to be when it gets warmed up.

I am looking for something that will drop idle speed, not raise it.

When I get some time I can throw my meter on the TPS and see how linear it is, and what base idle is set at. I really wont be expecting to see much. But may as well try it anyway.

I am off to the wrecker tomorrow. So, Ill grab some of every single sensor I can snag off a 3.4 from there. Then I can start the game of swapping parts and see what happens. Ill grab a different IACV and TPS while there. I hope to get to the bottom of this soon. For now though, it has not had any problems since I put the tranny treatment in, and some fuel injector cleaner. Maybe that fixed it? I dont know.

[86FieroSEv6]

At this point I'd like to see the fuel trim figures both with and without the symptoms occurring. Have you checked for electrolytic voltage coming from the cooling system (warm the car up, put one meter lead tip in the coolant without touching the radiator and the other on batt. neg., no more than a tenth of a volt should be present). If there is, it could be a bad ground or rotten coolant. Try "tap testing" the ECM, don't be heavy handed a light rap with a hard plastic object or even your finger tips would reveal a problem there. Wiggle test the harness by flexing it in the area between the engine and body where the most "flex" occurs during torque loads. To check for correct minimum idle air rate you have to seat the IAC. Ground the ALDL (A to B), key on engine off, wait till 12 has flashed three times then unplug the IAC. Turn the key off, remove the ALDL bridge and start the car. You may have to foot the throttle a bit to get started. Then slowly let off the throttle. It should be able to idle at around 500-600 rpm. Also, in a normal system, the IAC is not closed at idle. If the IAC is closed at idle and the system attempts to lower engine speed you will get an IAC related trouble code. On the scanner in road test data mode I like to see the IAC counts at around 20-30 hot idle in park/neutral.