89bonestockiroc

Hi, im having some trouble with my 89 iroc. It has an intermittent problem where it stumbles really bad and will barely run. The tach jumps from about 300 to 600 over and over and sometimes surges to about 1000rpm. It will recover sometimes then work fine. I drove it around for 2 weeks after it stopped, then it started again all of the sudden. Im guessing that it is some kind of ignition problem, but I was hoping that someone here has some idea what might be causing this. I put on new wires, plugs, fuel filter, cap and rotor, and o2 sensor and thought it was fixed. But it started again last night.
Oh, I almost forgot, its an 89 w/stock tpi and maf. It is not setting any codes.
Thanks
Mike

DANIELEK

Coolant Temp sensor, big vacuum leak?

89bonestockiroc

I have tried to locate a vacume leak but couldnt find one. I hadnt thought of the coolant temp sensor, but the problem is very intermittent, and it doesnt matter if im in closed or open loop. Most of the time it runs great, but every now and then it does this. If i hold the gas when its stalling like this, it pops and the rpm bounces a lot, and then it revs up like normal and may even run ok for a few minutes. Im really stumped on this one, and i cant trust my car to get me anywhere right now. It just drives me nuts because it runs so good when its not doing this. I am thinking about replacing the ignition module. Anyone else have any ideas on what could cause a problem like this just every now and then for a while? I really appreciate any ideas on what to look for.
Thanks

87transam5.7tpi

I'm having the exact same problems with my 87 GTA, I bought a IAC control motor today, I'm putting it on tommorow I'll let ya know what I find out. but since it happens to me one itme ant not hte next I'm hoping when I drive it tommorow it'll act up if it isnt' fixed.

89bonestockiroc

Hey 87transam5.7tpi, Im sorry to hear your car is doing this too. Its really frustrating. I am wondering about my IAC too, when I put the car in diagnostic mode , the iac motor never stops running. I have let it sit there and run for over half an hour and it never stops. If I touch it while its running it feels like its shaking a little bit. Does yours do anything like that?
The other theories ive come up with so far from endless searching of the archives is the ignition module or pickup coil , and maybe the fuel pump. I tested my car out again tonight and it still starts sputtering really slow and knocking, and the tach even sits at 0 for 5 seconds or so and then it revs up to 1500 or so and drops back down again, knocking and making noise the whole time. Please definitely post if the IAC fixes it or not.
Hopefully someone will post who has had this problem before and fixed it.
Thanks

greg_pl

on 99,9% it can be IAC Valve
( idle air controll valve - this second sensor on the
trothle under TPS - plug can be loose or dirty,moisture
- check connection, claen - I have exactly similary

89bonestockiroc

Hey 87transam5.7tpi, I was just wondering if you got your new IAC put on and if it helped your problem any.
Also if anyone else has any idea what can cause a car to act like this , please let us know.
Thanks.

ploegi

My car does this as well. However, mine will be fine when I first start in the morning, and run great till I let it sit for about an hour. Then, it will stumble, run rough, and generally sound terrible. I can sit and idle with my foot on the gas, just enough to keep the idle up at about 1K rpm, and then it will "fix" itself, rev to about 2500. When I let off the gas, it will idle normal, and run just fine.

I am fairly sure this is a "heat soak" problem on my car, but, I don't know which part is causing the problem. I have given the car a complete tuneup, and have even replaced the distributor. (yep, the whole thing.... although, it was a used unit..... had a spare in the garage)

Next is injectors I am thinkin'. Such fun......

87transam5.7tpi

ok I put on my new IAC motor last night. sorry I haven't responded till then. and so far it has helped. I have acces to a snapon scanner and before the IAC motor would hesitate and jump from 12 or so to like 60, over and over. now it is running like it is supposed to(the IAC motor) however I started the car like 5 times since then and not one problem. but like I said earlier it was doing it sparaticly, not on a consistent basis. but usally it did it ever other time to one outta 3 times. so far nothing though, I can PM you in a couple of days and let ya know how its working.

u r sofa king we tah did

my 89 tpi corvette did exactly what you are describing with the intermittant problem, the popping and slight backfire sound when you give it alot of gas while the problem is acting up. turned out to be a fuel pump. believe it or not, just hours before i got the pump changed, the car made a 600 mile trip without a single problem, then once i arrived it started running like crap again (it had been doing this off and on for a few months). after changing the fuel pump, it has ran problem free for about a year now.

89IROCkid

HI guys,

I had a similar problem with 89 TPI IROC, it turns out that the ECM was the cause of all the frustration.

At the time i could'nt understand what was wrong, the car ran fine one minute, and the next time it would'nt hold idle, would backfire like crazy and the mixture was so rich that the car was spewing out black smoke like a diesel truck. I also changed everything, cap, plugs, rotor, pickup coil, chip, EGR valve, IAC motor, all to no avail.

The ECM is'nt cheap, so i'd recommend finding another close f-body owner/friend and try his/her ECM in your car and see if that solves the problem before buying another one.

Good luck.