73 164 Rough idle after running 20 minutes

This is a scatter shot question since I don't have any specifics to provide other than after running the car for more than 20 minutes, it starts to idle rough. I can turn the engine off, then start it again and it will still idlel roughly, but after I run it a bit more it seems to smooth out. Starts fine and runs fine with lots of acceleration. I replaced an old fuel pressure regulator thinking that due to its extreme age, that it was causing issues. Does run much better, but the rough idle is there, but not as bad as before with the older fuel pressure regulator.

Any ideas would be appreciated. Thanks.

Steve

ssholland said:

after running the car for more than 20 minutes, it starts to idle rough.

Click to expand...

I'll assume you have a 164E (D-Jet Bosch)

Here is a tech manual on D-Jet

I would suggest doing a fuel pressure check. This tech manual says,

"D-Jetronic system uses constant fuel pressure and flow, so that only injection duration needs to be modified to control air/fuel mixture. "

If I was guessing, I might suspect auxiliary air valve or cold start injector is related. If cold start injector is leaking, or auxiliary air valve is not opening up, then both could cause a rich condition. You have suggested the condition does not change much with a change in fuel pressure regulator, and these two items affect air/fuel mixture.

But, you suggest when engine temperature rises, the problem disappears. Those sensors need to be tested.

One needs to go thru those test procedures...starting with correct fuel pressure...it must be set to OEM specifications.

Ok, I checked:

fuel pressure-good
cold start valve-good
auxiliary air valve-good

I think it might be a slightly clogged fuel pump filter and/or a slightly clogged fuel injector. I will clean the fuel pump filter and then run it with some cleaner for a bit and see what happens.

Check for vacuum leaks.

The intake manifold gasket, injector seals and injector stand seals are common problem areas.

Is your fuel pressure set to 28 psi as is shown in the tech manual on D-Jet 84B23F so kindly posted for you? If so, I think Volvo changed this to 30 psi. Hopefully, someone will correct me if I'm wrong.