300TE Idle too high - PeachParts Mercedes-Benz Forum

les_garten · #1 11-17-2010, 08:42 PM

I have a strange high idle problem on a '88 300TE..

It only happens when the car is warm and being driven for a while. Then the car idles about 1100-1300. No fun to hold back with the brake. It sat in the driveway tonight for about 20 minutes idling perfect. I has to be driven to really get it to act up.

Recently I replaced all the injectors, Inj seals, and holders. I replace the ICV hoses. New plugs, wires, cap rotor. Replaced a lot of cracked vacuum elbows. Replaced the "underside" rubber on the mixture control unit. Replaced the fan switch on top of the head, etc. Even cleaned out the throttle body.

The car starts well, better than it has for a while. Idles immediately at 900 when dead cold, then settles down to about 600-700. It sat for 20 minutes in the driveway at operating temp with this idle tonight. I used some mapp gas to try and find vacuum leaks and didn't find any. Listened with a stethoscope and didn't hear any. I looked for quite a while with the mapp gas.

When I had the mixture unit off I had the sensor plate out and wonder about it. So I shot some PIX with the car running. I guess it's centered, it "looks" ok to me.

I checked the rear temp sensor at temp and got 457 ohms. Does that seem right? It didn't change anything whether it was plugged in or not while hot.

I lubricated the throttle linkage and shot pix of it as well.

If I unplug, the ICV electrical connector, the car stops immediately, is that normal?

The only other issue is that somewhere along the line of recent "maintenance" I had the wheel off and the SRS light is on solid, won't go off. The bag is plugged in. I checked the Fuses on the OVP relay and they are good. Is there a way to check the relay itself?

So I'm kinda stuck here, any ideas where else to look?

http://www.turbonet.biz/misc/MB_Idle/AAA_2249.JPG

http://www.turbonet.biz/misc/MB_Idle/AAA_2250.JPG

http://www.turbonet.biz/misc/MB_Idle/AAA_2251.JPG

http://www.turbonet.biz/misc/MB_Idle/AAA_2252.JPG

http://www.turbonet.biz/misc/MB_Idle/AAA_2253.JPG

http://www.turbonet.biz/misc/MB_Idle/AAA_2254.JPG

ps2cho · #2 11-17-2010, 09:27 PM

I was thinking ICV and midway through your post you mention it dies when unplugged. I think you found the culprit. It should not die on you.
Here's my theory -- Your ICV is getting jammed open and when you unplug the connector the car stalls because the system is way out of mixture spec.

Start by removing it completely (2 bolts as you have probably seen) and shoot it clean with carb cleaner. You'll be surprised how much dirt and crap comes out....
Try that first and see if it fixes the issue. I have a feeling its whats happening.

The rear temp sensor only affects the mixture during cold start up. Leave it overnight, unplug the connector then start the car. You should notice it takes more cranks than usual. After the car warms up it does very little for mixture adaptation. It is all EHA, O2 sensor and potentiometer from there on out.

Easiest way to center the plate is to use two pieces of newspaper. A little reading here for ya:
http://w124-zone.com/?p=253

les_garten · #3 11-17-2010, 09:33 PM

Quote:

Originally Posted by ps2cho

I was thinking ICV and midway through your post you mention it dies when unplugged. I think you found the culprit. It should not die on you.
Here's my theory -- Your ICV is getting jammed open and when you unplug the connector the car stalls because the system is way out of mixture spec.

Start by removing it completely (2 bolts as you have probably seen) and shoot it clean with carb cleaner. You'll be surprised how much dirt and crap comes out....
Try that first and see if it fixes the issue. I have a feeling its whats happening.

The rear temp sensor only affects the mixture during cold start up. Leave it overnight, unplug the connector then start the car. You should notice it takes more cranks than usual. After the car warms up it does very little for mixture adaptation. It is all EHA, O2 sensor and potentiometer from there on out.

Easiest way to center the plate is to use two pieces of newspaper. A little reading here for ya:
http://w124-zone.com/?p=253

Thanx. I'll do that. I hate fooling with those ICV hoses!

I used the newspaper technique when I did mine.

les_garten · #4 11-17-2010, 09:45 PM

ps2cho,
I also noticed something that surprised me. There is a large rubber elbow that attaches from the valve cover to the aircleaner. It has a small vacuum tap off that goes to the fuel pressure regulator. I just recently replaced this because the original was hard and crumbly. I always assumed this was a crankcase vent to put excess oil fumes into the intake for burning. Basically a PCV. Mine has vacuum on it when it is dc'd from the aircleaner but connected to the valve cover. Is that normal? Sucks on my hand.

ps2cho · #5 11-18-2010, 12:54 AM

Quote:

Originally Posted by les_garten

ps2cho,
I also noticed something that surprised me. There is a large rubber elbow that attaches from the valve cover to the aircleaner. It has a small vacuum tap off that goes to the fuel pressure regulator. I just recently replaced this because the original was hard and crumbly. I always assumed this was a crankcase vent to put excess oil fumes into the intake for burning. Basically a PCV. Mine has vacuum on it when it is dc'd from the aircleaner but connected to the valve cover. Is that normal? Sucks on my hand.

Normal. If the diaphragm breaks in the FPR, fuel will be sucked in so just check for raw gas.