Rough engine while cold
Intermediate
Joined: Jul 2009
Posts: 445
Likes: 93
From: NY
Anything to be worried about? Idles just fine; but I get very noticeable vibration from the motor until it's started to warm up a bit. Then it's butter smooth.
Not the trans\axles because I can slap it into neutral and rev it and get the same experience of vibration.
98' with 123k on the clock. Super fresh car, been very well maintained.
Not the trans\axles because I can slap it into neutral and rev it and get the same experience of vibration.
98' with 123k on the clock. Super fresh car, been very well maintained.
You would rule out everything mechanical if the car drives properly when fully warmed up. I do not know of axles that could vibrate only cold.
So this is a temperature specific symptom that disappears reliably as the car warms up? Consider then, the temperature-specific systems that would cause this:
water temperature sensor
any of the oxygen sensors
AFM
and consider that the engine might be right at the edge of the smooth-running envelope at all times, but symptoms are only showing up when cold, such as a vacuum leak.
idle air valve hose, oil filler cap, pcv valve or any hoses, leaky v@lve cover g@sket (they can re-clamp up as the engine heats and expands, giving you a cold engine air leak only) (what the heck is this automatic link to E-b@y that I hopefully killed with "@" above?)
Colin
Last edited by Amskeptic; Jan 8, 2018 at 04:07 PM.
Pit Crew
Joined: Jan 2014
Posts: 181
Likes: 26
From: CA
Skeptic,
Thank you for those leads. My '98 also has a slightly rough idle both when cold and at operating temp.
I think I will replace some vacuum hoses first since they look a little cracked in spots.
It has been there for a year or so now. I thought plugs might take care of it , but I recently did those with no change.
Thank you for those leads. My '98 also has a slightly rough idle both when cold and at operating temp.
I think I will replace some vacuum hoses first since they look a little cracked in spots.
It has been there for a year or so now. I thought plugs might take care of it , but I recently did those with no change.
how noticeable is noticeable? I can sense very small vibes but it could just be normal road/tire conditions.
most drivetrain vibes are attributed to the transmission mount. easy to replace and gets rid of 80% of vibrations at speed, and they typically go out at that mileage.
if the vibes get stronger as the RPMs go up, then it's a rotating imbalance somewhere on the engine. check your fan, belts, etc.
most drivetrain vibes are attributed to the transmission mount. easy to replace and gets rid of 80% of vibrations at speed, and they typically go out at that mileage.
if the vibes get stronger as the RPMs go up, then it's a rotating imbalance somewhere on the engine. check your fan, belts, etc.
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Pole Position
Joined: Nov 2014
Posts: 3,254
Likes: 418
From: CALIFORNIA
While well maintained, the rubber mounts age-hard over time, here 20 years...
Does your AC compressor engage when cold?
Serpentine belt or driven components: What is condition of Tensioner pulley bearing, idler pulley bearing, Alternator (bearing-read my post on 130A upgrade), AC compressor clutch bearing (read my post) fan bracket bearing, fan clutch, Power Steering pump (they are somewhat noisy when cold-try using synthetic grade fluid...check out my post)....
Remove serpentine belt and inspect. While off, spin all the bearings and check for grinding or sideplay....the lubricant is 20 years old.....
Water pump, Idler Pulley Bearing, Tensioner Pulley Bearing?
If non-OEM parts were used then those items are suspect (read my posts on aftermarket water pump and timing belt issues)
Perhaps your harmonic damper pulley assembly requires replacement (rubber dampening ring hardened) or some ape changed the timing belt and used starter to loosen crank pulley bolt or chain and damaged rubber damper ring
Probably a combination of these items.
Racer
Joined: Sep 2008
Posts: 1,286
Likes: 212
From: Chandler, AZ
I had a symptom similar to this when first started after a long cold soak overnight, usually when temps are in the 20s-30s in the morning.
My engine was very loud but got quiet when warmed up. It wasn't a fan making a loud noise, but more of a mechanical noise.
It ended up being my idler bearing that was bad. When cold, it would not rotate as freely. But when warmed up, the tolerances expanded and the Boise went away.
I bought some new NTN bearings online and pressed them into the pulleys, for both the idler and tensioner on the serpentine belt. Cost was about $14.
My engine was very loud but got quiet when warmed up. It wasn't a fan making a loud noise, but more of a mechanical noise.
It ended up being my idler bearing that was bad. When cold, it would not rotate as freely. But when warmed up, the tolerances expanded and the Boise went away.
I bought some new NTN bearings online and pressed them into the pulleys, for both the idler and tensioner on the serpentine belt. Cost was about $14.
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jonny2k
LS - 1st and 2nd Gen (1990-2000)
5
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