Merc W124 - very high idle RPM

franksm

Hi folks

*apologies right now for the nerdiness of this thread, but I'm hoping it rings bells with someone who has "been there"

Car is a 1992 W124 230CE with KE-jetronic injection on M102.982 4-cyl 2.3 engine

I replaced the head gasket recently and put a new overvoltage protection (OVP) in. However, idle speed is now around 1500rpm rather than the usual 600rpm. Tried putting in the old OVP - same problem.

Am pretty sure I have all the pipework and electronics connected properly as before.

So I unplugged the ISCV (idle speed control valve) and the car is perfect, apart from being a pig to start when cold. Still getting between 24mpg and 28mpg around town.

Bad ISCV ? You'd think so, but it buzzes when given 12v, so that sounds like it is fine. Have checked it's getting 12v when the engine is running, and it is. It's a two-pin device - I traced the pink/blue back through the OVP and onto pin#1 of the KE controller. All good.

I traced the red/white wire back to pin#3 on the KE and that's good too. Am wondering if I damaged a sensor while previously working on the engine.

My KE is "KE0027", part# 006 545 7932 [07]

Thanks for any advice !

Frank

mike65

Does it have high idle right from the turn of the key?

This is either going to be a moment of genius, or stupidiy for even asking, but have you checked the idle adjuster at the end of the accelerator cable? Its the black plastic gromet thingy just by the micro-switch

http://img.photobucket.com/albums/0903/mike65/micro-switch.jpg

Mike.

franksm

Yeah, right from the turn of the key. Haven't tried letting it sit to see it it comes back down (does the KE system auto-learn ?)

That microswitch - it's completely closed (ie. throttle is completely resting on it). The throttle cable too is set right (tiny bit of slack)

I had the injection system apart during the rebuild, but I'm pretty sure I don't have any air leaks - if I did, they'd be apparent whether or not the ISCV was running or not.

mike65

I mention the cable cos when I had the 190e, one day I accidently turned the grommet thing and the following morning I started with a 3000 rpm idle! Started it twice, then copped what the problem was, tweaked the cable and it was back at 850 rpm correct for the m102 2.0 engine.

KE3 system does'nt learn anything, you learn!

Mike.

Mr.Diagnostic

Hi Frank.

From what you posted the ISCV is either opening too much because of a faulty input or it is opening the correct amount but there is some false air getting in somewhere. You need to check the TPS and idle switch first, then check for VAC leaks.

HTH

franksm

Cool - is spraying gas from an unlit torch around the inlet system a good way of finding a vac leak ? (gas would cause engine rpm to rise)

Just wondering why the motor is totally perfect without the ISVC though - very smooth and stable idle & acceleration; exhaust isn't smokey, sparkplugs are a good colour - neither grey nor black

Mr.Diagnostic

franksm wrote:

Cool - is spraying gas from an unlit torch around the inlet system a good way of finding a vac leak ?

that will work very well.......................as long as you manage to not blow yourself up!!!

That is a method which is used all over the world, safely or not. I use a smoke machine to find leaks from the inside out. Safest method would be to spray carb cleaner, though not entirely safe so tell your solicitor not to blame me if it all goes pear shaped.

Check the TPS, idle switch and throttle basic setting first.