My 84 has a stumbling feel to it when accelerating like the engine bubbles instead of revs right away.Once it gets going and downshifts (auto) it accelerates great. I was thinking it might be stuck in second.

So I did a vacuum test at idle. I got 16.5 wandering a little bit up and down, about a half inch but not consistently.

I tried pinching off vacuum hoses didnt get any change, and dont really hear any sign of air sucking anywhere.

When the gas pedal is depressed vacuum dropped instantly and bounced to about 22 inches when released, taking a second or two to drop back to 16.

It doesnt have terribly bad blow by, so I would expect atr least 18 inches but Im not experienced with these particular cars/engines.

Whats your best guess vacuum leak or timing off?

How do I determine?

 

spray some carb cleaner around all the vacuum line especially the one from the PVC all the way under the plenum

 

Have you checked base timing (timing with ESC disconnected), throttle position sensor voltage and the balance of the throttle bodies? All those things and marginal fuel pressure can be hesitation issues on a Cross-Fire.

 

Havent checked any of those yet, have to get a timing light I guess and learn how to check on this one.

Whatever it is it just started doing it. The car has a bad head gasket right now I put some blue branded head gasket sealer in it annd its holding ok but I dont plan on going out of town with it right away.

Today I took the air cleaning housing off to look everything over. I used a vacuum pump with a gauge to check the doors on the air cleaner housing and one door held vacuum and was able to be pulled close but the other one wouldnt hold vacuum or pull the door closed.

I found a bimetal sensor I think, inside the air cleaner housing and thats where its leaking at.The hoses were ok, the actuators in the doors are ok.

I was going to just hook vacuum straight to booth doors then I thought maybe thats not a good idea if they both shut. That could be the purpose of that sensor?

So I just hooked one up and left that one disconnected even though it means that door will always stay open.

The idle is back to almost where it used to be, 7-800 where it was always 600 or 700. But before I started today I noticed it around 900-1000.

Also looked at the vac hose that goes to the top of the pvc valve and runs to the canister purge valve I guess it is. I hooked the pump to that hose and it wont hold vacuum I heard gurgling from the canister.

I know I need to get a fsm just trying to get a grasp of things in the meantime, and its running a little better now. Halfway there I think.

Have to find out where that control vacuum for the pvc comes from why Im hearing that gurgling and if its normal for that hose to not hold vacuum with the engine off.

 

That bi metal sensor is part of the thermac system, it heats the air when the engine is cold to help in cold weather performance. If you live in an area or only drive when it's warm out, you can disable it.

 

I suggest checking the vacuum check valve. It is located next to the distributor on the driver's side. They are only $4 at any auto parts store, so it might be easiest to just replace it. This is what you're looking for:

 

is the engine stumbling at hard accelerating ? egr ? try to block off the vacuum to the egr solionid ! and do a general tune !!

 

I have a 91
I had the same problem.
Replaced the EGR Valve.
Not sure if your 84 has one or not.