Okay so a little backround on my 80 quattro. I just got done doing a whole lot of maintenance on it. This includes the lower intake manifold gasket, upper intake manifold gasket, valve cover gasket, cold start gasket, throttle body gasket, clean the throttle body, clean the cold start valve, did all the injector o-rings and cups, clean the injectors with seafoam and carb cleaner, new voltage regulator, clean all the wires to the alternator, new battery to body ground, along with the spark plug wires and a new air filter. I've also done the cap and rotor along with the spark plugs, fuel filter, coolant temp sensor and the o2 sensor within the last 6k miles.

So I got the car started yesterday after doing the first list of maintenance and it was giving me some odd problems. When I hit the gas the engine would stumble for a second and then catch itself and be fine. It only really would stumble with quick throttle input and this would only happen bellow 3k rpms. Above that it ran completely fine. It only stumbles when you first hit the throttle, after that its smooth a lot smoother. It does however feel sluggish and underpowered. When i take it out of the gear the idle will sometimes drop to around 500 rpm and then bring itself back up. The car idles funny and won't hold a steady rpm. It stays even for a second or two then drops then evens out and so on. I did spray carb cleaner around all the places that I thought could be pulling in vacuum though and it didn't seem to change the idle at all. The plugs are all white on the tip meaning that my car ran lean for quite some time. This makes sense though as the injectors where very dirty when i pulled them. The plugs were one of the first things I did when I got the car and im thinking they could have been fouled by bad fuel system parts. The car didn't misfire like this beforehand and im thinking maybe something I did brought out this problem. Anybody know of anything else that could cause a misfire like im having?

 

It's an air leak at the intake. One of your seals didn't line up right.

 

What year?

It does sound like an intake leak. Does your model have rubber intake boot on the throttle body that can be cracked while pulling it off?

DougM

 

Its a 1991 with a 10v inline 5 and yes it has a rubber intake boot off the throttle body to the fuel dizzy. This is a cis-e car also. I've tried spraying carb cleaner all around the intake boot as well. Im going to pick up a propane torch tomorrow and try to track down the vac leak with that. I've heard that works a lot better than brake clean or carb cleaner. Im also going to check the lower intake manifold gasket and make sure that's seated properly

 

So I went threw and sprayed down every inch of the intake system and all visable vac lines with brake clean then carb cleaner and I tried using the propane torch and I had no luck. Nothing will change this cars idle even the slightest bit. Im going to go threw it tomorrow afternoon and pull the lower intake manifold and see if maybe the seal didnt seat properly when I installed it. Ill also check the injectors and o-rings and make sure all of those are seated correctly. Its really the only other thing I can think of. Im so stumped by this. Any other methods or advice before I rip the hole thing apart again would be greatly appreciated.

 

I doubt it's a vac. leak especially if you just resealed everything. I'd be looking at the throttle switches. Also check that you reinstalled the ground wires on intake manifold. Other than that I'd say maybe the knock sensor if the CEL was flashing when it happens.

 

Nobody suggested you have a vacuum leak. We said you have an intake leak. Big difference, and not a job for propane torch or carb cleaner, unless you intend to set yourself on fire.

 

This car has no CEL being a 91. Is there anyway to check to see that the throttle switches are working properly? Also how about the knock sensor? Im assuming a volt meter would be the only way to check. That or would unplugging it possibly help and send it into a default mode like with the o2 sensor or the coolant temp sensor? I clean and reinstalled the manifold grounds. I make sure not to miss grounds and try to keep them clean as I know with vw's and audi's, especially cis cars, that they can wreak havoc on how it runs.

 

I have already checked and reseated the upper intake manifold gasket, as I said in my other post I will go threw and check the lower intake manifold gasket and throttle body gasket tomorrow when I have time to do so. I figured poking around for vac leaks wouldn't hurt incase that was my problem.

And no im not trying to set myself on fire, just trying to get my car operating normally again as its my daily and id love to have it back driving normally again.

 

Have you tried simply driving it around a bit?
DougM