Vehicle in question is a '91 Acura Integra. It has a manual transmission and 327,000 miles. Driveability is about as good as I can ever remember it being (bought new in '91). No hesitations, flat spots, sags, surging, hard starting, stalling, nothing at all like that. Idle has always been very smooth, at least as smooth as, or smoother than, the 4-cylinder engines in other and newer cars I've been in. Idle speed remains normal at a very steady 750 rpm. However... in the last half-year or so, the engine has started to have brief periods of warm idle where it idled noticeably slightly rougher than it normally did . These episodes were few and far between and seemed to have no connection to any obvious environmental circumstances. The episodes of slightly increased roughness have increased in frequency to the point where smooth idling is the exception. It also seems to me that fast idle (when cold) is a bit rough now as well. Fast idle was always completely glass-smooth. Part-warm idle has been noticeably rough for several years, but that always cleared up once operating temp was reached. I have noticed that idle roughness seems to be tied to ambient temperature. If the ambient is under about 70, idle smoothness is usually what I'm used to. The warmer it is, the greater the roughness. I can see nothing obviously wrong in the engine bay. The car is, IMHO, exceptionally well-maintained. Gas mileage is perfectly normal, and I do record that very diligently. I do not have a DSO or other equipment (other than a VOM) that would help me see what the many sensors are doing, so I'm asking here for ideas before spending money or contacting my guy, who is 50 miles away..

Tegger, YOU'RE asking this question!?!?! First thought, just off the top of my balding head, is leaky injector, possibly cold-start, if the car has one.

ben91932 wrote in news:2220da2f-e1ee-4b24-a5e0- I just checked them for cleanliness and good connections.

ben91932 wrote in news:a0002bdc-c7f6-4322-8c47- Valves have been checked. See my other posts. And especially see Steve W's reply.

Idle rougher when warm?

Aug 14, 2009 23 Replies

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ben91932 16 years ago

Tight Valves? (Sorry for all the tiny posts..) Ben

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Tegger 16 years ago

ben91932 wrote in news:2220da2f-e1ee-4b24-a5e0- snipped-for-privacy@c1g2000yqi.googlegroups.com:

I just checked them for cleanliness and good connections.

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Tegger 16 years ago

ben91932 wrote in news:a0002bdc-c7f6-4322-8c47- snipped-for-privacy@a13g2000yqc.googlegroups.com:

Valves have been checked. See my other posts. And especially see Steve W's reply.

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Tegger 16 years ago

"Steve W." wrote in news:h69l6a$f9h$ snipped-for-privacy@aioe.org:

How would one diagnose head cracks /without/ removing the head or manifolds? Not possible?

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