1999 E300 idle fluctuation - Page 3 - PeachParts Mercedes-Benz Forum

Murkybenz · #31 05-26-2017, 01:57 PM

Curiosity .. would bad earths cause this by affecting the ecu ?

packerfan · #32 05-26-2017, 10:51 PM

Quote:

Originally Posted by KarTek

Check the basics, make sure the throttle cable isn't too tight, not allowing the TPS to return to full stop.

The adjustment is right there at the TPS, couldn't be easier.

When I first got my car, the cable was really slack, causing a noticeable softness in the pedal. I dialed it in tighter, which improved things but I did notice that it was easy to get too tight and overcome the return spring on the TPS.

Which makes me think; I believe there are 2 springs on the TPS. Make sure one hasn't broken. I'm just going off memory but I think they are nested inside one another.

Thank you, I will check it out.

packerfan · #33 05-26-2017, 10:59 PM

Quote:

Originally Posted by jake12tech

Pretty sure idle speed is electronically controlled by your governor on the pump. The pump is half mechanical half electronic.

Thanks Jake,
I guess it's not worth worrying too much about as long as it keeps idling down when brake pedal is pressed before shifting trans.

jake12tech · #34 05-26-2017, 11:48 PM

Quote:

Originally Posted by packerfan

Thanks Jake,
I guess it's not worth worrying too much about as long as it keeps idling down when brake pedal is pressed before shifting trans.

Yeah not really too much, doesn't affect drivability. I eventually want to figure this out for myself. I replaced glow plugs on my '98 e300 recently. It had one bad plug and is doing the same thing as your car and my '99 e300. I believe there is something on the ECU that thinks the car still has bad glow plugs and raises the idle so it doesn't stall out at normal idle. I'll have to see if I can get a Mercedes scanner on it soon. I will let you know if I find anything out.

packerfan · #35 05-27-2017, 12:01 PM

Quote:

Originally Posted by jake12tech

Yeah not really too much, doesn't affect drivability. I eventually want to figure this out for myself. I replaced glow plugs on my '98 e300 recently. It had one bad plug and is doing the same thing as your car and my '99 e300. I believe there is something on the ECU that thinks the car still has bad glow plugs and raises the idle so it doesn't stall out at normal idle. I'll have to see if I can get a Mercedes scanner on it soon. I will let you know if I find anything out.

I think I may have solved the problem. I took a close look at the TPS and noticed a slight gap between the positive stop. You will also notice that the swivel ball at the end of the throttle cable is at an angle, the ball and socket are seized in that position (I will use penetrating oil and fee that up). I adjusted the nut on the throttle cable to slacken it until the gap closed on the positive stops. Started the engine and idle was right at 600 RPM!

KarTek · #36 06-11-2017, 09:43 PM

Thanks for the follow up, glad you got it sorted!