RPM's 'hanging' at cold start

[hansvdweerd]

Hello all!

Since about two months I have noticed that at a cold start my Ex idles a bit high in 'Park'. It also seems to pull a bit more when I drive off. This however is only for the first 50 meters or so. When you turn off the engine immediately and crank it again it doesn't 'stick'. This issue is present only once in a while... (a few times a month?). I drive my Ex daily. So most of the time it's fine. Otherwise I have no issues with the car.

The engine doesn't surge at all (idle is stable). About two months ago, when I think about it, I did have a DTC concerning the TPS (that the signal was out of range, I think). This didn't however cause the CEL to appear. After that I frequently scanned for DTC, but there were no codes.

Last February I replaced the upper and lower intake manifold gaskets and also the IAC-valve. I also checked for other vacuum leaks. A few months ago I replaced the stock airfilter for a K&N filter (no mods to the airbox, except last week when I removed the plastic pipe on the side of the airbox that didn't make much to me). Last week I also had the oil replaced.

Does anyone have an idea what could cause this intermittent issue with a temporary elevated RPM?

Thank you in advance!

Greetings,
Hans

 

[hansvdweerd]

RPM's 'hanging' at cold start (FIXED)

Hello all!

Since about two months I have noticed that at a cold start my Ex idles a bit high in 'Park'. It also seems to pull a bit more when I drive off. This however is only for the first 50 meters or so. When you turn off the engine immediately and crank it again it doesn't 'stick'. This issue is present only once in a while... (a few times a month?). I drive my Ex daily. So most of the time it's fine. Otherwise I have no issues with the car.

The engine doesn't surge at all (idle is stable). About two months ago, when I think about it, I did have a DTC concerning the TPS (that the signal was out of range, I think). This didn't however cause the CEL to appear. After that I frequently scanned for DTC, but there were no codes.

Last February I replaced the upper and lower intake manifold gaskets and also the IAC-valve. I also checked for other vacuum leaks. A few months ago I replaced the stock airfilter for a K&N filter (no mods to the airbox, except last week when I removed the plastic pipe on the side of the airbox that didn't make much to me). Last week I also had the oil replaced.

Does anyone have an idea what could cause this intermittent issue with a temporary elevated RPM?

Thank you in advance!

Greetings,
Hans

I replaced the relatively new IAC-valve with the old one (I kept it, because it wasn't broke) and the problem seems to have disappeared... I put about 2000 km on it (Holland - Switserland and vv) so far. My mechanic told me that the hydorcarbon rich gasses being let into the air intake manifold via the PCV-valve could cause the IAC-valve to clog and intermittendly stick.

Might cleaning the TB also have any effect?

 

[hansvdweerd]

Spoke to soon... NOT FIXED

I retrieved a pending DTC: P1504 (malfunction in IAC-valve).

This code is present when I have the old valve on and when I have the valve installed I replaced the old one with about 7 months ago in an atempt to fix a cold start issue (turned out to be the intake manifold gaskets). Do these IAC-valves go this quickly??

I checked if about 12 volts were going to the valve. I also checked if the resistance between the two terminals on the valve was between 6 en 13 Ohms. I also checked if the resistance between one of the terminals and the housing was greater than 10.000 Ohms.

This all checked out. Visual inspection of the valves showed little to no carbon built up.

So assuming the valves are okay, what other options are there?

I also noticed one thing: there was a hissing sound coming from the engine. But only when it's in gear. I noticed it because I had the hood open. I