shudder while idling

[Izual]

Hi!

Any help or advice is appreciated in advance.

I have an 87' NA 944 Auto

If anyone could give me some input on what could cause this i would be thankful!

while idling in drive at a stoplight the car seems to shudder every few seconds to the point where its actually becoming annoying. I dont believe it to be vacuum lines because ive had all of those replaced within the last year.

If while its shuddering you shift from Drive to Neutral or Park the shudder goes away instantly and feels normal.

Also another odd thing to point out is that i watched the gauges on my dash on the way home today and my car is equiped with an MPG gauge.

When idling the MPG gauge is pegged past 60 MPG and the car shudders. --EVERY now and then something will happen and the car will instantly change on its own. The shudder goes away and the mpg gauge dips down to 40 mpg where it stays solid.

I started to think idle stabilizer valve, but id like to hear other opinions.

Again this is only a problem while idling in Drive.

Temperature doesn't seem to effect when it does it. It seems to happen more when the oil pressure gets closer to 2 bar , but its started to happen at higher oil pressures as well.

[John_AZ]

Izual,
I think you may be correct about the ISV/ICV valve. Did you check the hoses to the valve when you replaced the vacuum lines. They crack at the bends.
You can check and clean out the valve. It is hard to get to with the intake manifold on. Replace the rubber mounts if they are cracked.

Some have had luck with just a flush of carb cleaner.

Here is one from TexasBlake--click in idle valve test.
http://www.texasblake.com/porsche/tech/icv.html
OR
Idle Valve

GL
John_AZ
1988 924S + 1987 924S

[cvriv.charles]

Do what john said. LOL. Stop hoggin all the questions JOHN!

[John_AZ]

Memo to self: Must spend less time on forums !!!!!
John_AZ

[cvriv.charles]

Originally Posted by John_AZ

Memo to self: Must spend less time on forums !!!!!
John_AZ

NO! You cant do that! we need you!

[John_AZ]

OK,

The MPG guage is jumping around. Even when the car shudders the idle stays rock solid at 850rpm (per Izual) . This new information may omit the ICV/ISV as the cause

The MPG guage may have a bad connection. In the tech info center above ^^ there is an article on how to cure some guage problems. I would first clean all grounds on the car, especially under the dash above the fuse/relay panel. Here is a list from TechnoDuck



Here is the link for the guage repair if you want to try

http://www.pelicanparts.com/techarticles/944_taillight/944_gauge_problems.htm

Another area to look at is the AFM connection. Clean the wire cable connection.
Here is a link to Clarks Garage for more info:
http://www.clarks-garage.com/shop-manual/elect-22.htm

GL
John_AZ
1988 924S + 1987 924S

[Izual]

"I wrote this article after having some strange readings on my instrument cluster – to include: fuel gauge reading ¾ full when I just filled the tank, voltmeter constantly reading 12 volts."

Another problem that ive had ever since i bought the car as well. So this looks promising!

thanks for the great info!

[John_AZ]

Izual,

HondaDustR just put everything about the MPG guage here-Post 8:
http://forums.pelicanparts.com/porsche-924-944-968-technical-forum/493325-econo-meter-fuel-consumption-guage.html#post4851496

GL
John_AZ