rough idle when the car warms up
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Newbie
Joined: Oct 2004
Posts: 20
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rough idle when the car warms up
I own a 1992 500 sel. When starting up from a cold start the engine runs pretty smooth while idling but after about 20 minutes of idling and the car starts to warm up the car begins to shake and idle very rough. If I give the car some gas a hear a popping noise (backfire) that appears to be coming from underneath the car. If I continue to give the car some gas, it will putter and then shut off. Could someone tell me what could possibly be the problem.
Super Member
Joined: Mar 2004
Posts: 640
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From: Granbury Texas(burbs of DFW)
a Few Nice cars.
My Uncles 89 420sel did the same thing and he took it to the shop,turns out ot be a bad set of wires(spark plug wires) and a distribtor(sp) cap and rotor.
Make sure your running 93 grade octane fuel.you might need a tune up or maybe a timing chain replacment?..get in into a shop before it becomes costly.
check the following
1-93 or higher grade gas
2-Check your coolent(could be running hot)
3-Wires and Spark plugs(tune up)
4-timing chain(should have been serviced @ 100k)
Make sure your running 93 grade octane fuel.you might need a tune up or maybe a timing chain replacment?..get in into a shop before it becomes costly.
check the following
1-93 or higher grade gas
2-Check your coolent(could be running hot)
3-Wires and Spark plugs(tune up)
4-timing chain(should have been serviced @ 100k)
MBWorld Fanatic!
Joined: Jun 2003
Posts: 1,179
Likes: 4
make sure idle control valve is clean, sometimes they get dirty and that causes bad idle. also clean the inside of the throttle body and throttle body plate, contaminants build up around the edge and prevent smooth closing of throttle plate. used throttle body cleaner for both procedures. takes noe more than about 20 min to do.
Almost a Member!
Joined: Oct 2002
Posts: 28
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From: california
w140
I Bet its the Mass air flow meter. Same exact thing happen to me this pass week. So I ohmed out all the sensors and replaced a few of the sensors including the fuel injector temp sensor and figured I would use the most expensive part last even though I was pretty sure to what it was. Sure enough it was the Mass air flow meter, or what ever MBZ calls theres. I paid 300 bucks for it at the dealer which I though was reasonable compared to ones Ive purchased for Jap cars. . Also when an Injector gets warmed up it can cause surging when idling. Check the EGR valve fif its holding suction.
