pscottjr

Car starts fine, idle is pretty steady most of the time.

However, when I increase rpms and then let off the accelerator the rpms drop to 0 then after about 1-2 second go back to normal idle (it does not stall). So, every time I shift gears I wait a second to let idle get back to normal to engage clutch (makes for a smoother shift). This drop happens at all increases of rpms (1000-4500).

Is this normal or if not where should I look to correct this problem? I have had the car for less than a month. I will have to check the PO records to see if and when he last changed the fuel filter, fuel pump.

BPG_Austin

Parker, I don't know anything about ealier cars but I support taking off the fuel filter checking it. I did this for good measure on my s4 when I bought it. New filter and check valve came from Roger. There was considerable resistance when blowing through the old filter. Throttle response was better after changing it out. It was an easy job to do, at least in the s4.

Best, Ben

85fortheDrive

Yep, cheap and very doable.

nosnow

My 82 does the same thing. I have not really done any investigative work, I just leaving my foot lightly on the gas during shifts. There are threads on this and it seems like there is a Vacuum limiter that is either disconnected, gone bad or you have a vacuum leak. Apparently the limiter gets disconnected to help with throttle response as it does not allow the RPM to drop quickly. I'm sure there is a more knowledgeable person who can chime in.

I'm going to start my intake refresh in a month so I'm interested in finding out the solution... if there is one.

pscottjr

Ok, I will change the fuel filter.

Paul, If you find out anything please post up. I thought about a vacuum problem, but would not know where to start looking. I did a search, but may have used the wrong subject when searching the subject.

thanks

anonymousagain

Idle Switch...

https://rennlist.com/forums/showthre...ferrerid=37511

pscottjr

Interesting thread. I like what Enzo said

"Vacuum limiter is the disc on the side of the TB (not sure if the auto’s have one). When you close the throttle, the engine vacuum bleeds air past the throttle plate via the vacuum limiter. This keeps the rpm’s from dropping too fast & keep the engine from creating too much vacuum. Something about emissions or something is what this is for.

I had mine removed a long time ago (3 years?). When I would close the throttle in neutral, my car would almost die, rpm would drop to zero then bounce up. I discovered (via Porken) this is from the idle switch. This switch totally cuts fuel for a brief second. This combined with the vacuum limiter prevents un-burnt fuel from dumping out the tail pipe. So remove one, disconnect the other.

It annoys me when the rpm’s “hang” between gears. Removing the vacuum limiter corrects this. "

I will check out this weekend and report back. This may be a vacuum limiter problem and an idle switch problem. Not sure how to approach this. Free up the idle limiter. test... P O R K E N???????