rough idle
09-15-2003 | 03:16 AM
#1
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Junior Member
Joined: Aug 2003
Posts: 2
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Car: 1991 trans am gta
Engine: 350 tpi
rough idle
ok everybody here's what i got for you.
car info
1991 firebird trans am gta
350 tpi engine with the following mods
runners, headers, and exhaust
ok now here is the problem im having
my car had a rough idle and would start to stall at stops when it was warmed up after i had driven it about 10mins. and it seemed to lack performance (in comparison to my friends 91 camaro with the exact engine and less modifications). So went to get it checked out and my #2 cylinder was misfiring so i got new plugs, wires and a new coil all made by MSD. after installing it all it ran the same and seemed to be getting worse so i decided to park the car and reviewed some posts on the message board here at third gen to see what else it could be. so first i adjusted the TPS with no results and then i tested my injectors and found 3 that had bad coils so i took my plenum and runners off and took the injectors to a shop, had the three replaced and the rest cleaned and flow matched. while i had everything apart i tested my EGR valve and sure enough it wouldn't hold a vaccum so replaced it with a new one. now i have everything back together and the car has stopped stalling at stops(so far) yet it still has a rough idle and lacks performance and im not sure what to do next so.... any input on the problem would be great and ill answer any questions the best i can. thanks in advance
car info
1991 firebird trans am gta
350 tpi engine with the following mods
runners, headers, and exhaust
ok now here is the problem im having
my car had a rough idle and would start to stall at stops when it was warmed up after i had driven it about 10mins. and it seemed to lack performance (in comparison to my friends 91 camaro with the exact engine and less modifications). So went to get it checked out and my #2 cylinder was misfiring so i got new plugs, wires and a new coil all made by MSD. after installing it all it ran the same and seemed to be getting worse so i decided to park the car and reviewed some posts on the message board here at third gen to see what else it could be. so first i adjusted the TPS with no results and then i tested my injectors and found 3 that had bad coils so i took my plenum and runners off and took the injectors to a shop, had the three replaced and the rest cleaned and flow matched. while i had everything apart i tested my EGR valve and sure enough it wouldn't hold a vaccum so replaced it with a new one. now i have everything back together and the car has stopped stalling at stops(so far) yet it still has a rough idle and lacks performance and im not sure what to do next so.... any input on the problem would be great and ill answer any questions the best i can. thanks in advance
09-15-2003 | 01:54 PM
#2
Supreme Member
Joined: Jan 2003
Posts: 4,248
Likes: 228
I've had bad luck with aftermarket ignition components. In fact, I just found out over the weekend that my four-month old MSD coil was bad. So I put the stock one back in. In fact, I'm running a totally stock ignition system and it seems to be ok.
If you have a scanner, it would go a long way to help diagnose the problem.
You may want to reset your idle speed and verify that the idle air control motor is functioning properly. Do a search for idle speed adjustment in the archives.
Have you put a vacuum gauge on the car? Make sure you have good vacuum- I would imagine at least 19 inHg for a stock cam (I was getting 18 inHg with my ZZ4). Also, with the engine idling, temporarily pull the vacuum line off the MAP sensor and see what the engine does. If there's no response, you likely have a bad sensor.
If you have a scanner, it would go a long way to help diagnose the problem.
You may want to reset your idle speed and verify that the idle air control motor is functioning properly. Do a search for idle speed adjustment in the archives.
Have you put a vacuum gauge on the car? Make sure you have good vacuum- I would imagine at least 19 inHg for a stock cam (I was getting 18 inHg with my ZZ4). Also, with the engine idling, temporarily pull the vacuum line off the MAP sensor and see what the engine does. If there's no response, you likely have a bad sensor.
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