I have a 91 Trans Am 305 and tuned port. I have recently been having a rough idle and by rough I mean it acts like it is ready to go and raises up. My RPM goes from 300 to 1500 in repeating intervals until it finally stalls on itself. She'll fire right back up but I have to prime it (turn key, sit and then turn over fully.) If not she wont start.
I have changed all the intake gaskets and changed a few vacuum lines that were cracked and such. No more hissing from vacuum leak. . Also changed Thermostat, air filter, TPS sensor, (Cleaned) IAC valve, o-rings on fuel injectors and finally the fuel filter.
This all helped for a bit... But it came back.
I'm wondering if it is my fuel pump or maybe another vacuum leak. If any of you have an idea or similar problems and found a solution please tell me. I need this running like stock before I begin to work on her.

I will give further info if needed.

 

300 rpm sounds like its hitting the stall speed in the PROM so it kicks back up. So think what would make idle drop to that level? Vacuum leak? Fuel flow? Bad IAC? Other stuff?

 

you changed the orings on the injectors but are the injectors stock?

 

Yes, stock injectors. I wish they were after market.

 

check the fuel pressure - should be around 40 w the engine running. changed the injectors - were they flow tested?

 

Still sounds like a vacuum leak.

https://www.thirdgen.org/forums/post...823-post2.html

 

Vac leak, also I would go ahead and change the Coolant Temp Sensor and check timing.

 

I'll be checking the fuel pressure in the next couple days. I have a friend with a gauge. But, I warranty'd out my TPS sensor because one of the pigtails was completely gone from the damn thing. That helped a ton, doesn't die on me like it did but still a rough idle. Also fixed another vacuum leak.

Does anyone have a vacuum diagram? I can't find one in the repair manuals I have and tried google. :l

 

Your vacuum plumbing MIGHT be correctly routed as is.

Even if not, you don't need it just yet, to find more leaks. Were you able to follow the detection procedure? After finding the one leak, does it still lope idle?

If it still does, you likely have more leaks. THey're hard to find, but you HAVE to find them.

 

Turns out my TPS sensor was a P.O.S. so I warrantied it out and running a lot smoother than before!! . But still idles hard only stalled on me once so far. I found another vacuum leak going to the EGR valve don't know if I mentioned that or not. But fixed that as well.

In 3 weeks going to do a tune up with new spark plugs and wires. I'm wanting to use bosch plugs and ACDelco wires, any reccomendations?

 

Maybe before unloading $ for those parts, get the O2's live readings in a scan. If they are steady, you're getting a good burn with the plugs and wires now...

Give the TPI article a read-though, that I posted.

 

Okay, I saved the money and decided to try the cheaper approach and try a different air filter. Made a world of difference! It will occasionally stall but only when I give to much gas. But other than that she is running better.
Getting new plugs. wires and distributer cap when I put in my cam. That'll be about a 1/2 year-year

 

I firgured out my problem for anyone that wants to know. Since the cooler weather I noticed my car ran it's best before it got to 180 degrees.
But as she finally got warm there the problem looms, my idle starts to go all out of wack and eventually she stalls and starts backup.

Well, I thought why not flow test my damn injectors. Come to find out the cylinder 1 and 2 injectors are stuck open. Dumping more gas than it should, my O2 sensor apparnetly couldn't keep up or understand what was going on so it was over compensating and thus creating the surge in my idle.

Replaced them, and i'm all good now! Hopefully this information will help someone else.