Problem with clutch/idle

[Zrun]

I noticed this problem only when taking long trips.

 

I'd drive at 120kmh for a long time, and when I'm about to get off the highway, I step on the clutch and shift to neutral and let the car coast.

 

However, the RPM of the car sticks at 3000rpm even after I'm coasting. It happened for a few seconds, and I rev it abit and it drops back down to proper idle rpm.

 

How do I debug this? Got to do with my idle control, CAI?

Edited August 24, 2004 by Zrun

[Bernard_2]

Get back to your workshop seem is your engine problem.

[Ace_t]

I do get a similar experience quite similar to yours.

 

mine is auto and when I let the car coast (in gear) , the rpm would stay above 1k RPM like the pedal is still being stepped.

 

When I actually step on it, the RPM responds upwards then goes down to idle RPM...

 

could not figure out what was the cause, even after changing some major engine components..

[Hoppe]

based on my experience, could be due to :-

 

1) Exhaust problem. I used to have this problem and it was mysteriously solved after I removed the Cat convertor. Maybe the inconsistent flow of air caused by the blockage of the CAT caused the engine to respond by maintain a higher rpm until the "throat" gets cleared by another rev?

 

2) Spark Plugs. I changed my spark plugs at the same time when I removed my CAT. The spark plugs were burnt black and the idle problem was "gone" after the change of plugs. I have had use a lot of fuel additives in the past, so that could cause the spark plugs to "burn" faster.

 

Dunno which actually solved my problem. But has to be either one, since I didn't change anything else.

 

But I think every car will experience idling rpm problem after some time. For carburetted car (old car like mine), can retune back. But not sure about new fuel injected types.

 

Note : I also noticed that switching between different RON type of petrol can caused idle to increase sometimes. Maybe the ECU is adjusting?

Edited August 25, 2004 by Hoppe

[Ace_t]

1) my car has no CAT. Pre 92 model. But from what you mentioned, perhaps my muffler is clogged up already.

 

2) My plugs are still clean. Using iridiums.

 

You correct in saying that the ECU is adjusting for petrol RON changes. Maybe this is the real cause for RPM to remain high at idle for a short duration.

 

Perhaps it's even the throttle cable being abit sticky.

[Hoppe]

another problem could be the clutch. Maybe dying soon. This is the worst case.