i have a 89 trans am that originally came with a 305 and tpi, i swapped out the 305 w/ a 350 and 24# injectors, i got a chip from tpichips and car ran great for months,i wanted to run faster so i put an lt1 manifold on, ran fine for months.
My heads had exhaust ports that the intake would not cover up, so i took the intake off fixed that and replaced the spark plugs and wires, since then it started running like crap.

What is does is when i first turn it on its fine for like 3 mins, then it sounds like i have supercharger under my hood, my air filter is sucking in so much air at idle its really loud, when i give it some gas it bogs down then revs up, at a still rpm lets say 3k rpms it backfires, when the car warms up it does the same. Sometimes after the car is at its normal running temperature and i turn it off, it wont come back on until it cools down.

I have replaced the distributor cap, rotor, module, spark plugs, wires, coil, i have checked for vacume leacks, my compression is 170 across the board.

I'm starting to think that it might have something to do with my custom chip, i did have my battery unhooked for about 2 weeks. did it get untuned somehow?? or is my MAF bad?

It started doing it after i fixed the intake and replaced the plugs for the first time but as mentioned i have replaced them again.

Please help, i am frustrated and i'm almost at the point of slapping a carburator on it

 

Looks like you have done the blanket fix like I done lately but one of the last fixes I did on my '88 was the IAC valve. Try that reset procedure and unscrew it and verify that it is 1 1/8 inch from the shoulder of the IAC to the end of the pintle. Mine was off about an eighth so I replaced it. Helped a lot but my big difference came when I replaced the distributor and done the base timing deal. Looks like you already been there. Hope that helps.

 

Take a can of carb cleaner and, with the car running, spray it around the intake manifold gaskets. If the idle changes, you have a vacuum leak.

 

wow, i really did not think about that one sensor, i dont know if this will make a difference or not but i do not have the water lines going to my throttle body.
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done that! thanks for the advice.

 

I think the water lines are there for heating the TB for economy purposes, not so much for function. Somebody correct me if I'm wrong. I'm just not sure. I know in the summer, mine is turned off because the heater line shuts off so it closes off the TB supply and it's been fine. Sounds like your CTS is working and that's why the 3 minute wait.

When you remove the IAC for measuring, be sure to clean inside the TB port it came from. Oh yeah, when you clean the IAC, hold the pintle downward and spray the cleaner. I was told it is a stepper motor and you do not want that gummy crud leeching down into it. New ones are $50 so be carefull.

Please update what you find. Anxious to hear about it.

 

Are you sure you have the timing set right????

 

yeah its def. not a timing problem, weve rechecked that like 4 times

 

so i took the IAC off and measured it and cleaned it, it was 32.2mm, the little retractable thing was stuck so i had to force it in, now its the right size. It was realy dirty as well so i cleaned it. put it back on.

I did adjust my TPS since i had time, it was a few degrees off.

Started the car up and its still doin the same but now it idles at around 1500rpms.

took the chip out to see if anything changed, it ran the same as before.

I will be buying a new IAC and see if it does anything, ill keep you guys updated.

 

At least the idle came down a bit... you hit something good. Also, by cleaning the IAC port out real good there will be more flow so the computer won't think it needs to open the valve more. That's the way it was explained to me, anyways.

You mentioned the TPS was "a few degrees off". By that you mean it is now measuring .54 volts at idle position, right??

 

actually my idle rpm went up to 1500, before it was around 8-900.

yes my tps is now at .54 @ idle and ~4.30 @ WOT

 

Sorry, I misread the 3k rpms in your first post. A good IAC will re-learn where it is supposed to be from ECM feedback. I don't know how it does it but my new one started a high idle and within a few minutes it had stepped down to 600. Running out of options here. You done went thru my other possibles.


Your base timing 4-6 degrees??

 

just an update, the car is still bad. i will get my chip reprogrammed and see if that does anything.

 

Another easy test... Remove the PCV and power brake hoses. Plug those ports to assure ZERO vacuum leaks there. Do same for any other vacuum hoses you see and then crank it up. If that fixes your problem, hookup each hose one at a time until the problem comes back.

Also check you thottle body for a carbon ridge where the plates nest. A ridge could prevent the plate from fully closing.

A while back mine had a whistle where a piece of the TB gasket sucked in and leaking. Hope that helps...