Engine surge?

**Y2KBird** · 12-12-2011, 09:52 PM

Its been a long time since I've bee around here but stuck on a problem with rpms while decelerating. Car has plenty of power in 1st, 2nd, 3rd, and 4th. As soon as I pop it in neutral while decelerating the engine revs. Betweeen 1500 and 500 rpms. Once the car comes to a complete stop it evens out and idles smoothly at 7 to 800 rpms. I've done some searching but failed horribly. Any help or suggestions would be greatly appreciated. Thanks

**WS6SP33D** · 12-12-2011, 11:40 PM

Pop in neutral while decelerating? Not really understanding. Any time you throw a car in neutral when coming off high rpm's it will jump up then come back down to normal due to less load. Also have you checked for vacuum leaks? More details would be great. Good luck

**Y2KBird** · 12-13-2011, 12:29 AM

The tach bounces consistantly from 500 to 1500 in 1 second intervals until I come to a full stop. Shifting in to neutral as in coasting in any gear to a full stop then the engine ceases to basically rev itself and idles at a normal speed. It surges to the point accessories, heater, and and lights dim. The car is basically still stock, no aftermarket amps or odd lighting drawing any amp load. I have wondered on occasion if the car was going to just die on me comng to a stop. I checked the car originally for vacuum leaks and couldnt find anything. The car also isnt showing any codes. Just thought it was odd since acceleration isnt suffering and idle isnt suffering, just decelerating. I'm stumped at the moment.

**pajeff02** · 12-13-2011, 03:35 AM

Check for a dirty throttle body, dirty or malfunctioning IAC, and for vacuum leaks in the PCV system that could be allowing excess air into the engine. Is your SES light on?

**0rion** · 12-13-2011, 03:52 AM

how long since you cleaned the MAF sensor? I would clean that and the throttle body like pajeff said. Sounds like an air metering issue to me.

***SMWS6TA*** · 12-13-2011, 01:12 PM

In addition to what Jeff & Orion had stated I have one question: Is this for a T/A or Formula (V8) or a Firebird (V6)?

I ask because the idle is set differently between the 2 motors. (You indicated you have a Firebird in your info)

**Lunatikgixxer** · 12-13-2011, 01:24 PM

Mine did this kind of when my spark plugs were bad. But i also have a cam. Check those next if you cant find any vacuum leaks.

**JayTA98** · 12-15-2011, 08:34 AM

agree with all posted. have you done any regular maintenance to the car? how many miles?

**Smittro** · 12-15-2011, 08:41 AM

Also if it's a 2000 and up 3800-II there is no IAC, TPS, (fly by wire TB) and the PCV is located inside the upper intake manifold..

Also there could be an issue starting in the tranny..

My 01 3800 a4 would serge forward slightly on cold start up even though it was in park.

Not an automatic expert but I felt there was an issue starting in the valve body or seals/solenoids.

**JayTA98** · 12-15-2011, 08:47 AM

Originally Posted by Smittro

Also if it's a 2000 and up 3800-II there is no IAC, TPS, (fly by wire TB) and the PCV is located inside the upper intake manifold..

Also there could be an issue starting in the tranny..

My 01 3800 a4 would serge forward slightly on cold start up even though it was in park.

Not an automatic expert but I felt there was an issue starting in the valve body or seals/solenoids.

there is our V6 expert

**Smittro** · 12-15-2011, 08:55 AM

Reason I mentioned the tranny is because rolling in neutral there could be a partial pressure bleed off happening causing it to "think" it's still slightly in gear.

**DRVWS6** · 12-15-2011, 07:46 PM

Mine is doing the exact same thing... but I have a mutha thumper cam, a TPiS LS6 intake manifold with a 92mm throttle body, 41lb fuel injectors, 1.8 ratio rocker arms, full length Hooker Headers, and a Magnaflow exhaust... My SES light came on and it was throwing 02 sensor codes... so i replaced both and it went off and everything seem to be fine for a little while... then the surging started happening again... i've checked for vacuum leaks, cleaned the maf sensor... replaced the iac valve and still does it... i dont know if it needs re-tuned or something? car has 34,xxx miles...

**0rion** · 12-16-2011, 05:08 AM

Originally Posted by DRVWS6

Mine is doing the exact same thing... but I have a mutha thumper cam, a TPiS LS6 intake manifold with a 92mm throttle body, 41lb fuel injectors, 1.8 ratio rocker arms, full length Hooker Headers, and a Magnaflow exhaust... My SES light came on and it was throwing 02 sensor codes... so i replaced both and it went off and everything seem to be fine for a little while... then the surging started happening again... i've checked for vacuum leaks, cleaned the maf sensor... replaced the iac valve and still does it... i dont know if it needs re-tuned or something? car has 34,xxx miles...

with your mods that could be a tuning issue.....who tuned it?