I've got an '87 Trans Am with the 350 TPI. It stumbles under light throttle and sometimes even "pops." I just bought the car about a month ago. I checked the plugs and they seem to be fairly new. I changed the fuel filter also. I'm not sure about the cap, rotor and wires tho. The wires are not factory. I'm wondering if the timing chain is worn out or if it's time for a valve job?

 

Same issue with my '85 TPI. It only happens under light throttle. If I stomp on it then it runs like a champ. I'm leaning towards a fuel pressure and/or vacuum leak issue. Although I've looked EVERYWHERE for a vacuum leak with a can of carb cleaner and have found nothing.

 

i had that.. put in new injectors.. works fine.. i posted my problem, all i got was to change every part in the car.. why not injectors, they only put the fuel in the engine..

 

your tps sensor could be bad or might jus need adjusted

 

I don't want to hijack Michael's thread, but for me I've put in a new TPS and adjusted it. The problem still persists.

irocuroc, injectors may be my problem, but I would really like to not have to spend the money on new injectors. I'm still praying it's some inexpensive sensor or vacuum leak. Oh well, Murphy's Law says that I'll spend $1000 replacing every f_ing sensor on the car, and then another couple hundred bucks replacing the injectors.

 

Hey guys my 87 trans am does this too. it only does it and i mean ONLY when i come to a stop at a stop sign and slowly roll through it like half stop then go. It kinda wants to die then it goes. ????? does anyone know the problem?

 

My87T/A,

You just summarized my problem EXACTLY! It's only at a stop and it's in the low RPM band. If you find the answer to this then let me know and I'll do the same. I've been working on it for a little over one month now and I'm starting to track down what it IS and what it IS NOT. Let's stay in touch.

 

Sounds good. right now i'm only 15 and trying to work and get money to keep the car in good running shape. I plan on changing the runners and base, and porting the plenum. But that is not important.

 

yuor base idle sounds high and as well the TPS might be miss adjusted to it to set base idle use the A B jumper same way to get codes count to 30 slowly turn it off the unplug the IAC then pull out the jumper and star the car this will put u in base idle after you have it set turn the car off plug the iac back in the set the TPS and it should work right then... its happened to me a few times

 

im gonna go try that. thanks i hope it works. Will i be able to tell if it does that unless i drive it?

 

Not sure but my guess is no. I think you will need to drive it to see if it stumbles down low. I unplugged my MAF and the car still drove like crap, so I'm pretty sure that my MAF isn't the problem. I'm thinking it's either fuel or vacuum related. Let us know how it turns out.

 

well it worked for me......idk how long it will last but the car is runnig fine now. i switched back over to the bad 87 maf and it still idles weird and runs rich but i cant afford a new one or even a good used one right now.

 

Try unplugging the EGR solenoid and drive it for a bit.. My neighbors 89 Chevy truck, granted it is a TBI 350, but it had the exact symptoms and this fixed the problem... It may be worth a shot...

Jason

 

If you dont want to just replace your injectors you can rule out half the battle with them by measuring their resistance. I would do it cold and then hot and see if any of them are out of spec. Should be around 11-13ohm.

 

take a step back here guys. We can't diagnose this over the internet. Here's the basics. From what he said I'm assuming the car stumbles and pops under light load at steady speed. This is almost certainly caused by too much ignition timing or a lean fuel mixture. Start with the basics. We know there might be a timing issue or a lean fuel issue. First thing to check is make sure the base ignition timing is correct, 6*BTDC. If the ignition timing is not advanced too far, check for things that could cause a lean condition at part throttle. a vaccum leak, clogged or dirty injectors. If the TPS was bad it would also have a really bad off idle stumble as well and he hasn't mentioned that.

Ohming out the injectors proves nothing about their spray pattern which is the concern here. For not much money you can send the injectors out to be cleaned and flowed, most places do it for something like $80.

Again, keep it simple and solve the engines problems. Don't fly off the handle diagnosing everything without the facts.

 

Are injectors hard to replace. I'm assuming they're not. What are a good set of injectors to use for a stock motor?

 

I too have almost the same situation. Mine does not do it all the time and it comes and goes. I will be driving and then all of a sudden I can feel it coming on so to speak and it will start stumbling or missing. My temp gauge doesnt work so I am not sure if it only does it in closed loop or not. Does yours do it all the time? What are the symptoms of a bad or sluggish O2 sensor? I think I need to get a cable from Moates because I would just be shotguning parts in and that would be expensive.

 

Mine has only done it maybe three or four times if that but right now i have a brake light wiring problem so i cant even drive it.

 

Not that I know everything about forum troubleshooting, but....

I dont know how long it has been since you had a tune up, but I just did new plugs, cap, rotor, wires, coil, fuel filter, Timing and Oil Change. Wanted to start fresh, and it fixed more little oddities than I can tell you. Start with the timing, then shoot the vacuum lines with WD40, and see if the RPMs rise, that will tell if you have a vacuum leak. Then start the tune up process.

 

heres where me and my little club member go. you can get a set of ford svo for 134. with a 3 yr warrantee.. good guys
www.fuelinjectorconnection.com ask for jon tell him frank iroc sent you.

 

well i only have 67000 miles on it and i changed plug wires and air filter and random stuff. but i havent done a full tune up.

 

I HAD THE SAME THING HAPPEN WITH ME AFTER I REPLACED THE DISTRIBUTOR AND DID A MAJOR TUNE UP.--IT MADE ME SECOND GUESS EVERYTHING THAT I HAD DONE.--I WENT BACK DOUBLE CHECKED EVERYTHING TWICE. AND IT WAS STILL RUNNING LIKE CRAP --FROM TIP IN THROTTLE TIL ABOUT 18-1900 RPM.--BUT--I AM GLAD I SAW THIS THREAD!-- I TOOK RU-QUICK'S ADVISE AND TOOK A LONG HARD LOOK AT MY EGR.---I DISCONNECTED THE VACUUM HOSE AT THE PORT COMMING OUT OF THE INTAKE AND PUT A PLUG ON IT. MY TPI CAR HAS NEVER RUN BETTER! THE 40 MPH BUCK AND STUMBLE IN 4TH GEAR IS NOW GONE. SO FAR NO CHECK ENGINE LIGHT HAS COME ON.--I REALLY DON'T WANT TO FOOL WITH REPLACING THE EGR BECAUSE IT'S SUCH A PAIN TO GET TO.I'M GOING TO RUN IT LIKE THIS FOR A WHILE AND SEE HOW IT DOES BEFORE I PLUG IT BACK IN.

 

I like your approach to troubleshooting and have a question for you.

I have an 89 IROC 350. The car has had some problems. Got them ironed out except one. If you slowly crack open the throttle just a little bit it stumbles and almost dies. If you are cruising on the highway with the throttle just cracked you can feel it stumbling. Open the throttle a bit more and it smooths out.

Changed all the injectors and ignition module which fixed my other problems. It has a new fuel pressure regulator (changed it when doing the injectors).

I have had no success with service shops. They all seem to be clueless about this car.

Do you have any suggestions?