rest rpm fluctuation
 

Have a 97 LX, at start it is fluctuating on idle between 2K and 3K rpm, after engine warms up its at normal 400rpm. I hear its somewhat of a common thing but what causes it? car has 230K miles on it.

Re: rest rpm fluctuation
 

First, you need a tach that isn't lying to you. The one on the dash apparently isn't very accurate.

Hot idle speed should be around 700 rpm.
They surge between 2000 and 1200 rpm repeatedly when certain conditions are met.


Here's a few possibilities off the top of my head:
Vacuum leaks could cause it.
Sticking IAC could cause it.
If it has a thermal operated warmup idle speed device, it needs hot antifreeze flow in order to work properly.
Someone messing with the wrong adjustments could cause it. Base idle speed, for one. Jacked throttle stop for another.
So could wrong parts, there are differences between A/T and M/T on some of them.
Skewed CTS could cause it.
Probably more.

Re: rest rpm fluctuation
 

Yea the car is manual transmission. I would have to find the manual and see the difference in the parts between the MT and AT. Any tips on helping identify the issue or just kind of check down the list type of matter here.

Re: rest rpm fluctuation
 

Why sure. A list I make isn't a list of junk to replace, it's just a list of possibilities to check.
Got a scantool that can display an engine data list?
Got any codes? Fix that.
Inspect for vacuum leaks. Fix that.
Measure TPS, should be .49v @ CTP. If no, then TPS is outta whack or someone jacked with the throttle stop. Fix that.
Base idle speed set correctly? (That means more than just "check the idle speed".)
Does it have a warmup speed device separate from the IAC? Is it getting good hot coolant flow? I see clogs in the water line fittings sometimes, that restricts coolant flow and makes the valve take too long to warm up.
Is the IAC the only idle speed control device?
Is the IAC sticking when cold?
Is the CTS accurate and reporting true values??

Re: rest rpm fluctuation
 

Don't quote me, but I believe MT came with a two wire and AT a three wire IACV.

Also, the FITV was eliminated for 96-00.

Re: rest rpm fluctuation
 

Thanks. You're right on both accounts.
I can't remember which has what unless it is right in front of me so I can see it. After a ton of years, they all become a blur.

Also, I just looked on the parts diagrams and I see 3 different versions of intake/TB/IAC. One for LX and lower, one for EX-MT, and one for EX-AT.

Re: rest rpm fluctuation
 

unfortunately did not get a chance to take a good look at all the things this weekend. recommendations on a diagnostic tool for the CPU at a reasonable price? Don't really have anything to grab all the codes with