Here's the scenario -

When I leave work in the afternoon, I drive out of the lot, and it's 1/2 mile before the first stoplight. Everyday for the past month, without fail, when I reach that stoplight, the engine drops revs to maybe 200, rebounds to normal, and continues this cycle every 5-10 seconds until I get going again. Of course, it's not noticeable anytime other than this first stoplight or at idle. Oddly, in the morning when I head out, I have about 1 mile drive to the first light, and I haven't noticed it doing it at this time. Maybe something about higher ambient temp and cold engine temp, I dunno. Either way, the dealer said they could not duplicate the problem. Ideas?

It could be a vacuum hose loose . I had a problem last week with the engine speed occasionally (not all the time) dropping to about 400 rpm when in D or R which caused minor shaking of the car. When in N or P, the rpm's would rise to about 1500, drop to 500 and kept repeating this every couple of seconds on its own. I was changing some wires underhood over the weekend and found a couple of vacuum hoses had poped loose. I put them back where they belonged and no longer have the problem.

But it only happens when cold, and a vaccuum hose wouldn't care about temp, I wouldn't think.

What year is your 202? My car does a very similar thing but only once a day. In the morning I drive 2.5 miles to work (lucky me). At the light in front of my office, every time, almost without fail, after sitting there for a few seconds the RPM willdrop momentarily to below 500 RPM and then will level out again and that is the end of it. Considering the car has an air pump and EGR system I have been assuming that this is something to do with the emmissions control system turning on once the car has warmed up a certain amount. This is just a guess of course. But with all the computer decision making going on in this car I have started to call it HAL.

Mike

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

mine's a 97.

...but did the dealer pull the codes?

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

No codes according to dealer last visit that would reflect a problem. There were climate control codes, which were used to fix a separate issue, but nothing related to the cold idle issue. Oh, and it did happenn this morning, so I dont believe ambient temp has any effect.

I am still thinking something in the emmissions control system, and I meant engine temp not ambient. In my old Supra I would always get EGR surge but only when it was cold. Even if I am right about the emmissions system, there could be something else exacerbating the problem such as plugs or something. The vacuum hose idea is a good one also althoughg benzdude doesn't say what car he has. My C230 doesn't have nearly as many vacuum hoses as my old car. I think a lot of them have been replaced with electronics.

Mike

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra