Surging idle at operating temp 83 944

Ace78 · 07-08-2020, 08:05 PM

I’m hoping someone can give me some advice as I’m at my whits end. I have a surging idle when my 944 gets to operating temp. To make a long story short there’s a Venturi tube under the intake with a line that runs to the break booster & the line wasn’t connected. When I covered the Venturi tube opening with my finger the idle stopped surging.

Well I got excited & thought I finally found my problem, but when I hooked the line from the break booster back to the Venturi tube, the idle went all haywire again. The line seemed ok from visual inspection.

Hoping someone might be able to help me out, I need to get her passed smog ASAP, thanks guys!

Bigtoe32067 · Bigtoe32067's Garage

Sounds like the diaphragm in the break booster is leaking causing a vacuum leak.
Do the brakes work fine or are they hard to press?
If you hold the pedal does it slowly go to the floor?
If you connect the hose to the booster does pressing the brakes affect the idle surge?
Tony

Ace78 · 07-08-2020, 08:35 PM

Thanks Tony. This is an old problem & I haven’t driven the car in a long time, but don’t remember an issue with the breaks. Just replaced the gas & fired it back up the other day. I’ll double check the breaks tomorrow.

dcmachinist · 07-09-2020, 01:45 AM

Brakes

Sent from my SM-G955U1 using Tapatalk

OK-944 · 07-09-2020, 05:03 AM

When this started to happen on my (now sold) 85.5, it turned out to be the ICV (idle control valve) located just underneath the intake manifold. I first tested the ICV with a 9v battery (easy test...can leave it installed for this step) and found it to be unresponsive...so I removed it, and after seeing the price of a new one, went ahead and rebuilt it...and then all was well with the idle.

pfarah · pfarah's Garage

It's known as the Aux. Air Regulator on the early cars.

mytrplseven · mytrplseven's Garage

My bet is also the ISV (idle stabilization valve) It's buried under the intake manifold. While I was going through the engine on my 951 I chose to replace it (O'riley's auto parts sells them) along with installing all vacuum lines and getting rid of the venturi with a Lindsey kit. I am now solid as a rock. Taking the manifold off sounds like a major project, and the first time it is, but once you've done all this you never have to chase this stuff again.

Ace78 · 11:19 PM

Mytrplseven - will the Lindsey kit fit my non turbo 944?

Ace78 · 07-11-2020, 11:19 PM

Ok-944 - I hooked up the aux. air regulator to a 9v & it slowly closed. Thanks for your comment.

Ace78 · 07-12-2020, 10:35 AM

So the breaks feel good & no change in idle when pressed down. I noticed a blue tube on the line from the thermo valve to the vaccine valve & felt around on it. I must have pressed a bit on it because the idle changed. Squeezed it off & the idle issue stopped. Unfortunately the car shut off shortly after & wont start. Any thoughts?

Ace78 · 07-12-2020, 02:07 PM

All right, disconnected the battery for a while & it started back up. My plan is to get a Lindsey delete kit & a new auxiliary air regulator while I’ve got the intake manifold off. Hopefully that will take care of the problem. If not, maybe a new dome....thoughts?

Jfrahm · 07-12-2020, 02:37 PM

This sounds a bit strange. What to the plugs look like? I wonder if the FPR or damper is blown.

Ace78 · 07-12-2020, 03:27 PM

Jfrahm - I don’t have the manifold off yet: hopefully this weekend if I can find a reasonable aux air reg & get the Venturi delete kit by then.

pfarah · pfarah's Garage

Good luck on the "Reasonable" part. I think you can find a rebuilt one for @250 or so...

Jfrahm · 07-12-2020, 04:36 PM

Manifold? I was wondering about the spark plugs. If it would not restart after plugging a vacuum leak I wonder if they are black as the ace of spades.

Ace78 · 07-13-2020, 08:29 PM

Jfrahm - oh. Haven’t checked the plugs out, but at least it starts now.

Ace78 · 07-13-2020, 08:31 PM

So Lindsey Venturi delete won’t work with a NA, but at least I did find a complete vacuum hose kit from 944 online, going to grab a refurbished aux air regulator from them too. Hoping this will fix the issue!

rwererds · 08-26-2020, 06:09 PM

I noticed a blue tube on the line from the thermo valve to the vaccine valve & felt around on it. I must have pressed a piece on it due to the fact the idle changed with the best table saw. Squeezed it off & the idle problem stopped. Unfortunately the auto shut off shortly after & wont begin. Any thoughts?