924Board.org

Greenie · Joined: 10 Aug 2004 Posts: 13 Location: Seattle, WA

Have a very nice 87 924S that I took over from a relative. Has a true 35,000 miles. Went ahead and did whole front engine job even though it seemed o.k. Also did complete "tune-up" with plugs, rotor, cap etc...

My only issue is a rough idle. Here's the rundown.

Idles rough (lopes), but above 1200-1400 rpm it purrs very nicely.

At idle, if you pull plug wires, it gets worse by pulling #2, #3, #4. But, if you pull #1 at idle, nothing changes, still the rough lope, but not any worse (telling me #1 isn't firing at idle)

If I give it a little throttle to up the idle above normal (2000-2500 rpm) and repeat the above procedure of pulling plug wires, it has a noticeable effect with all #1, #2, #3, #4. So, this tells me that above idle, #1 is firing and contributing???

The car is nice and smooth running on the road, it's just that idle that's giving me trouble.

I had the injectors cleaned and verified by an Injector Doctor. I'm at a loss and would appreciate any insight.

Could the injector just not be working at low pressure??
Is it as simple as changing the Idle Speed Regulator??
Fuel Pressure Regulator or Damper??

Thank you very much for any feedback.......

Diesel · Joined: 03 Nov 2002 Posts: 1061 Location: Ellington,CT

Check for a vacuum leak at that cylinders intake runner first, then get back to us.
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Dan Flanagan--2002 VW Jetta TDI, 83 Mercedes 300D,83 Mercedes Euro-240D

Greenie · Joined: 10 Aug 2004 Posts: 13 Location: Seattle, WA

Sorry for the Ignorance, but could you lead me in the right direction to check this???? What am I looking for and where??

Diesel · Joined: 03 Nov 2002 Posts: 1061 Location: Ellington,CT

Where the intake manifold enters the cylinder head is a gasket that seals vacuum. If there is a vacuum leak it will make a misfire especially at low engine speed. Easiest way to check is to run the engine and spray carb clean around the gasket. If the miss goes away or the idle changes you've found a leak.
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Dan Flanagan--2002 VW Jetta TDI, 83 Mercedes 300D,83 Mercedes Euro-240D

Gram · Posted: Tue May 10, 2005 8:25 am Post subject:

I had a similiar problem. When I had the injectors out I noticed one of the head inserts was loose (coincidentally on No. 1) I tried tightening it with the correct-sized allen key (hex spanner) which I found in the car tool kit, but it didn't seem to want to tighten and I chickened out in case it shattered and bits ended up on top of the piston. I just ran a bead of RTV silicone around it and it has cleaned up the idle. I'll probably have the head off one day so I'll replace it then. Maybe there isn't quite enough vacuum at idle to suck it all in tight?
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'82 924 NA Euro (hers)
'98 Audi A4 TDI (ours)