Hey all. Some of you remeber the problem i was having with my car. For the ones that do not I have a 1994 Trans Am GT M6 w/ 104,000 miles with the following mods: Star Spec Stage 2 Clutch, Star Sped Billet Flywheel, LT4 KM, 1LE Elbow, Arizona Speed & Marine CAI, and Gutted CAT. The issue i am having with my car is hard to explain, i will try my best: At low RPM the car surges and seems like it is getting to much air, or not enough, hard to tell. It will surge until 2000 rpm and then its fine after that rpm. It does it when the car if first started, and getting worse when it is warmer. Its horrible when its warm and you come to a red light, and so to take off (not fast) it will surge and gotta give it some gas to get it to go and then once 2000 rpms hits if you dont let off abit the tires will spin. Below are the things I have changed in the past 2 years:

Plug Wires (twice, MSD's in there now)
Plugs (twice, gaped at .50)
Coil
Opti Spark
Radiator (fixed my overheating issue)
PCV Valve
and the normal hoses, belts, oil changes, and tune ups were done.

Between the things above i replaced and the mods to the car, nothing has fixed the issue. Alot of people told me I could need a valve job because the valves were not seating propery. But the mechanics i talked to all told me that was not the case, and that the motor ran extremly smooth and did not shake at all and that could not be it. I am leaning toward TPS, or somehting along with the Trottle Body, any ideas all? Anyone have this issue?

-Nick

 

Did you check the IAC? That would be my first guess. After that, the TPS and then the MAP sensor.

Greg

 

Not to sound dumb, but did you replace you fuel filter? My was cloged and I made to same problem. Check your fuel pressure,too. Hope that helps

 

Where is the IAC and is that Idle Air Control sensor? and yes M-Man, i did change the fuel filter. I forgot to add that. Another issue with my car also is a delayed start for some off reason, it will crank sometimes for a few seconds and then kick over, its not how it should be. Ideas on either issue?

Scream And Fly: Can you link me to a pic of where the IAC is?

 

This is from Shoebox's AWESOME website: http://csce.uark.edu/~jgbertr/rb/iac3.jpg

Greg

 

GREAT thanks, what do they cost about?

 

Also can i have pics of where and what the TPS and the MAP sensor look like. Thanks.

 

When your car surges, does your oil pressure surge as well?

Does your oil get dirty relatively quickly (500 miles)?

 

I'd try someone else's maf to see if that's the problem also..

 

All kinds of pics on my Tech Page.

Also, I wonder if you might not have a temp sensor problem. The one in the water pump feeds the reading to the pcm. Some scan data would easily tell you if this is a problem. It really sounds like you need to get some data so that you can intelligently determine the problem. You might waste a bunch of money throwing parts at it.

 

Gripenfelter the car surges and the oil presure when the car first start is up there, i think 60's, and then it drops as the car gets warmer. At idle at mid temp its almost at 20, but when you rev it, it also goes up. Shoebox GREAT site, thanks alot. I dont think it is the temp sensor in the water pump becuase, i forgot to add: I replaced the waterpump when i did the optispark :-) Any other ideas? I think I am gonna rep the IAC, MAP, and TPS whatcha think? Somehow i dont think that will fix it but atleast it will make me feel better, lol. Anyone?

 

this sounds alot like the low rpm stumble many (including myself) have complained about...

Not sure if this would work but a few no-cost things to try and find the problem.

1. Check the egr valve, attach a vacuum pump to the vacuum port and verify that it still holds. Also make sure the diaphragm still moves. a faulty egr valve could cause surging when driving.
2. Once the car is warm and exhibiting the problem, unplug the MAF to force it into open loop. Drive it around and see if the surging still happens, if it doesn't you may be able to narrow the problem down to a problem with the MAF, O2 sensors or the computer.
3. Clean the throttle body, gunk buildup behind the blades could cause the car to act up when taking off from a stop..

 

I belive i tried unpluging the MAF when it warmed up about a year ago. That didn't fly. Although, the EGR sounds interesting. Should i replace the EGR, MAP, IAC, and TPS? lol

 

I'd pull the EGR and IAC; inspect and clean them and the throttle body.
For the EGR, make sure the diaphram moves freely by pushing on it while the engine is off.
If you have a scanner check the IAT sensor and the TPS. Make sure they're not tap sensitive. Try tapping on them with a screw driver handle while idling.
The IAT (intake air temperature plugs into the elbow) I noticed that moving IAT to where the air filter is and off the elbow made a big difference in accelaration after sitting at stoplights.
The TPS (Throttle position sensor) is on the Throttle passenger side just above the IAC.
You might also try as a test to run the engine without the accessory belt to determine if the alt,powersteering,ac or tensioner are spinning free.

I doubt its the MAF,WaterTemp,Oxygen sensors since problems on any of these would also affect higher rpms and closed loop(Warm engine) operation.

On my car at about 40Kmi I was getting surges for about 3mos before the Optispark crapped out. Oddly it was covered by GMs 5/60 smog warranty.

 

just a note, I pulled my egr thinking it might have been stuck, and found that the plunger/stopper was actually broken off of the stem connecting it to the diaphragm. Replaced it and fixed my gas mileage and surging at highway speeds.

I keep wondering if the fuel pressure drops momentarily, causing the surging/hesitation... Have you checked yours?