95 964, 154,400 miles.

The car has developed an intermittant rough idle when the engine is hot.

Observations :

On cold starts the engine doesn't run up to 1,500 rpm immediately, then down to ~800 rpms now. It starts just fine but it starts and stays at ~800 rpm right from the start.

The rough idle is only noticeable in Neutral and when the engine is hot.

Engine vacuum is very good throughout the engine temp range.

The engine idles smoothly in gear.

It doesn't always idle rough in neutral when hot, but most of the time it does. It will idle smoothly then you can feel it shake once in a while then it will just shake constantly, throw it into gear and it smooths out.

There is an intermittent cylinder miss when you listen to the exhaust only when the engine is hot. It is not a regular miss and is defintely intermitent. Sometimes worse than others.

What I have done:

Checked for vacuum leaks, none found.

Cleaned the flame trap, IAC valve and the throttle body.

Ran injector cleaner thru the fuel system and changed spark plugs (this did seem to made the rought idle a little less severe and slightly less frequent), I've checked this over several days so it's not my imagination. So a slight improvement but since I did both at the same time, I don't know which had more of an effect.

Any thoughts are appreciated.

DEWFPO



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1998 S90 071,245 and 1995 964 154,100

The problem has actually gotten worse, the miss is now consistent and it is one cylinder. I was planning on pulling the coil wires one by one to find the offending cylinder but on a lark I grabbed my propane cylinder and stuck the nozzle between cylinder runners 1 and 2 and opened up the valve and to my surprise the miss went away, turned the valve off and the miss came back. Repeated it again to make sure I wasn't halucinating, checked for a miss at the exhaust and confirmed I now have a intake manifold leak either in runner 1 or 2.

#$#%^)#(*_# (to put it politely)

Now, how to fix....

DEWFPO
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1998 S90 071,245 and 1995 964 154,100

If you have a high speed internet connection, I'll send you some pics. Mr. Bay 13 himself replaced my intake manifold gasket. He didn't take out the intake manifold but instead unbolted it, moved it back a little, replaced the gasket and bolted it back together.

Much more simple than removing it.
--
"Socialist practices are now so ingrained in our thinking, so customary, so much a part of our mores, that we take them for granted." Leonard Read, 1951

Thanks TRM,

I do have a HS connection, I sent you a P.M. that you can send the pics to.

Much appreciated.

DEWFPO
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1998 S90 071,245 and 1995 964 154,100

The fix is simple, just a few tough spots. The nut that holds the bottom of the intake manifold is a bear to get in and turn it loose. That nut doe not need to removed, just loosened, the bolt that is part of the intake manifold just fits into a slot.

A word of caution when you reinstall the fuel rail, where the three bolts screw in, those thread are easily stripped. Though I do remember someone telling of their mechanic that does not remove the whole intake manifold. Maybe that person will chime in. I would though and replace the seal on the oil trap/ or replace the hoses. Get an injector seal kit from the dealer too.

I could fax you the pages from my book tomorrow if you would like. Just send me a phone number.

DanR 94 964 266,000 miles (32,000 on the new engine)
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DanR

Thanks again DanR,

Is that bottom manifold nut best accessible from the top or bottom? How long did it take you to replace the gasket? On your car, was it the gasket against the head or the black rubber sleeve(s) that was the problem on your car? I am lucky enough to have the Volvo green manual so I've got the 'official' write up. It's always interesting to see the difference between the green book instructions and folks that have done the repairs themselves.

Again, Thanks for your offer.

DEWFPO
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1998 S90 071,245 and 1995 964 154,100

Dewfpo, sorry about the intake gasket, probally the toughest part to have to pull and replace, great thinking though on finding the culprit causing your problem. If you cleaned up around the area where the leak is ,would some Fel Pro Ultra Black gasket compound work for a short time till you got yourself ready for this adventure? Stuffs pretty durable. The intake gaskets used during the year your car was produced have given many a 960 owner greif.
Good Luck
Poolman

Thanks Poolman,

I thought about trying a temp. fix with sealer but I can't get anywhere near the offending gasket to even try to patch it up without substantial disassembly. I wish I could.

You know, it sure would be nice to have a smoke generator to easily track down these sorts of leaks, but they are so expensive and finding a use don is very difficult.

I appreciate your repsonses.

DEWFPO

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1998 S90 071,245 and 1995 964 154,100

Hey again Dewfpo
A smoke generator is no problem,
A good Havana,Three to Four feet of clear 3/4 inside dia. flexable tubing
and a match, if it don't work you still have the Havana.
Poolman

I like that !

DEWFPO
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1998 S90 071,245 and 1995 964 154,100

An occasional misfire and you seemed to cover most of the possibilities. How about a coil that is starting to go bad? The fuel pressure regulator? A bad connection somewhere, part of my annual maintence is cleaning and tightening all but a few of the connections under the hood. Even the big plug from the engine harness to the ECM. A compression test and leak down test would rule out wear to the mechanicals. You might just have to wait and see if it worsens before finding the answer. Just a few of my thoughts.

DanR 94 964 266,000 miles (32,000 on the new engine)
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DanR

Thanks for your thoughts DanR. If I pull the vacuum hose off the FPR should I see a change? There's no fuel coming out of the regulator and at idle, pulling off the vacuum line creates no noticeable change.

I've been leaning towards the coils/wires as a potential source. I can't imagine the fuel injectors just acting up when the engine's hot, although fuel pressure can be a problem. I need to get a adaptor for my fuel pressure gauge to attach to the fuel rail.

DEWFPO
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1998 S90 071,245 and 1995 964 154,100

Hello Dewfpo,Hope your well,You may be on to the problem with the coil pack idea,if there is a way to tell which cylinder is causing the problem,or buy just one and swap out till it's gone away.If there is an injector going bad that would be a little tougher. Back at 190k on mine I pulled the injectors and sent them to a co. that back flushes them while they are pulsed and then tests them for proper flow. Cost me 150 plus UPS one way, but made the injectors almost new again,they even check the coil circutry for proper tolerances.
How about the idle air valve I know you've probally cleaned it, but could it be giving up the ghost. Would the one on your other car fit to test it out?
Just grasping at th straws that may help.
Thanks for your help in the past and good luck.
Poolman