1999 firebird stalls on deceleration

[jackpot149]

First post on your site. Hopefully y'all can help out. My sons 1999 Firebird, 3800 series II stalls on deceleration. Went thru this sequence of tests -
1) accelerate to 25-30 mph, hit brakes, engine stalls when RPM drops to near idle (700 RPM). RPM spikes briefly to about 1000-1200, then dies.
2) accelerate to 25-30 mph, place in neutral (automatic), RPM drops to idle OK, hit brakes, engine stalls in same manner
3) accelerate to 25-30 mph, place in neutral, RPM drops to idle OK, coast to stop, engine runs OK

Just realized there's no idle air control valve on this engine, will be cleaning throttle body tomorrow. Was able to clear EGR code that was thrown with a new EGR valve. Changed fuel filter, fuel pressure checks out OK.

Any thoughts or suggestions would be appreciated.

[vanbibber]

Re: 1999 firebird stalls on deceleration

any other codes coming up?

you should have a IAC valve, do a search iirc someone posted a picture of where its at. if i remember correctly the 00+ didnt have them.. i might be wrong on that though so dont hold it against me if im wrong.

other things that come to mind.. MAF or MAP sensor maybe?

[jackpot149]

Re: 1999 firebird stalls on deceleration

Its sort of unclear to me about the 99's. Based on the pics I've seen, there's nothing on engine that looks like it. Been up and down the manifold and throttle body, no IAC or anything that looks close (unless its hiding!!)

Recently replaced exhaust system with headers, new cat, cat-back system, but stalling occurred before that. Did have a cat failure code and the mechanic suggested we change it out. Since my son had purchased the exhaust system, we went ahead and installed it. No change with respect to the stall, but it sounds much nicer!!

No other codes however.

[vanbibber]

Re: 1999 firebird stalls on deceleration

hmm.. have you checked fuel pressure?

[redbird8628]

Re: 1999 firebird stalls on deceleration

check for vac. leaks. thats what it sounds like, since it seems that it happens when you hit the brakes, clamp or plug off the big vacuum line going to the brake booster, and take it for a easy ride. stopping with out the vacuum assist is going to be like stopping a train. the diaphragm in the booster could be ripped.

[v6mOtOrhEAdftOp]

Re: 1999 firebird stalls on deceleration

I'd say MAF or vaccum leak. If it's slamming the car when it downshifts (that's if it is an a4)? If so, then I'd bet on a vacuum leak. Otherwise, i'd day MAF sensor

[jackpot149]

Re: 1999 firebird stalls on deceleration

The fuel pressure checks out OK according to the mechanic. Can't be sure he checked it while driving however, so perhaps just a static check.

The car has an automatic tranny.

I'll definitely check for vacuum leaks, along with cleaning the throttle body. I understand they can get gunked up some over time from EGR. The brake vacuum line is an interesting suggestion. Worth a shot as well.

Then I can checkout the MAF.

Thanks for the suggestions so far. I'll let y'all know how it comes out.

[jackpot149]

Re: 1999 firebird stalls on deceleration

Just an update - after school, sports, and generally doing anything else but work on the car, we finally got back to it after my son couldn't drive it any longer. After checking for leaks and changing the MAF, plugs, wires, cleaning the TB, all with no success, I broke down and took it to second mechanic. He was able to diagnose the problem with the fuel pressure regulator. It was leaking internally. Changed out and voila', no more stalling. Apparently the first mechanics who said the fuel pressure checked out missed something!!!

Thanks for the help and insight.