300E - Hard Starting when Hot
 

I just bought my first Mercedes last night, a 1986 300E with 93,000 miles. The car is in excellent, almost like-new condition and runs flawlessly except that it doesn't want to start when it's hot. I just now started it for the first time this morning, and it started easily within 1-2 seconds, ran up to about 1100rpm for a few seconds and then settled down to about 800-900 rpm. As it warmed up, the idle came down to about 600-700 rpm. The idle seemed pretty smooth after the first 10 seconds or so. The car just had the 90,000 mi. service at a Mercedes dealer in January, so all of the adjustments, filters, fluids, etc. were taken care of.

After it's hot and it's been shut off for maybe 15-20 minutes though, it doesn't want to start cleanly. If I keep my foot off the accelerator it will mostly just crank over without even trying to fire, and if I give it any gas it will stumble a bit and finally catch on maybe the 3rd or 4th try, usually with half to full throttle. It runs rough for maybe 5-8 seconds and then settles into a normal idle and runs cleanly.

Are there any diagnostics I can do without any special tools to try to track down the source of this problem? Any likely common, inexpensive possibilities?

I haven't bought a service manual yet. Which one is recommended, the factory manual, Haynes, Clymer,...?

Thanks for any help,


Gary

Try the SEARCH facility.

Hard-starting-when-warm M103 SOHC motors has been discussed literally hundreds of times.

Hi Gary:

Welcome, and enjoy your 300E! The search for words like 'warm', 'idle', 'start', '300E' will turn up a lot of threads - one of the better is http://www.peachparts.com/shopforum/tech-help/22347-300e-rough-starting-when-warm.html?highlight=warm+hard+start+300E . It also has links to threads by Benzmac on this issue in the responses, so click on those as well.

Enjoy your ride!