My 93 300E with 3.2 four valve ran great all winter. Once it started to get warm out, the idle began to surge from almost dying to about 1500 either after idling in traffic or heat soaking for a bit after parking. When it was somewhat cool out the car would begin running fine once it cooled a bit. I have read numerous posts on this problem but nothing I read in any of those worked as I have replaced or checked the things recommended in those posts.

Now that it's over 60 always, the idle surges from almost a kill to 1500 or so all the time. It also seems like it's running lean on take off and at speed. I have replace fuel filter, plugs, OVP, checked for vacuum leaks and found none. The upper wiring harness appears to be almost new.

Before I bought the car a significant amount of work had been done at a shop. I don't know the details but the MAS appears new and like I said before so does the wiring harness.

When I first got it the spring that helps close the idle micro switch was broken and the idle was accordingly high. I have repaired that.

The fuel pumps are a bit noisy and I have ordered new ones but I don't know whether that could even cause the problem.

Any hints from anyone as to what the problem could be.

Is there a point at which I have to worry whether the car will get me home?

Likely the throttle motor (actuator), either the part itself or the internal or external wiring.

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I don't think mine has that. It has a throttle cable.

It is still drive by wire, I agree with Gilly.

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90 300TE 4-M
Turbo 103, T3/T04E 50 trim
T04B cover .60 AR
Stage 3 turbine .63 AR
A2W I/C, 40 LB/HR
MS2E, 60-2 Direct Coil Control
3" Exh, AEM W/B O2
Underdrive Alt. and P/S Pulleys,
Vented Rear Discs, .034 Booster.
3.07 diffs 1st Gear Start

90 300CE 104.980
Milled & ported head, 10.3:1 compression
197° intake cam w/20° advancer
Tuned CIS ECU
4° ignition advance
PCS TCM2000, built 722.6
600W networked suction fan
Sportline sway bars
V8 rear subframe, Quaife ATB 3.06 diff

The SFI cars have the electronic throttle. The cable you see is for emergency running mode, or limp home mode. Will feel like pressing on a rock and will be lucky to get the car going 15 mph with it, meant mainly as a "get me off the railroad tracks" mode. This sort of answers the last question on your original post.

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If you look under the intake manifold over on the drivers side you will see the throttle motor.

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I tried to check the codes and I could only get a reading from pin 7. The light on the recirculate switch in the interior was blinking as well but I don't know how to read that.

I got codes 2, 23, and 30. I have almost no confidence in that. Neither pin 8 nor pin 14 would give me anything - the light wouldn't even turn on.

My car does not have ASR so I think the throttle motor is only for cruise. Maybe I am wrong but I intend to take look it over well tomorrow. I'll take it out unless it looks like it's been replaced. Is it possible for me to repair that unit if the wires are bad? If I replace it do I need to have some programming done by the dealer?

I tried replacing the spark plugs and noticed the connector end of one was very corroded and the connector from the coil to the plug was kind of deteriorated. The bolts holding the cover on, which also hold the coils in place, were all stripped out, so I helicoiled them. It didn't help. I thought maybe the coils were loose. I did not replace the connector because I couldn't get one right away.

I drove the car today and really lost power about 10 miles down the road. Now it seems to be missing badly. I suspect the coil or that connector but I'm still pretty stumped.

I appreciate all the input.

Bob, recommend replacing all 3 coil to spark plug connectors.

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Fred Hoelzle

the throttle motor is NOT just for cruise, you need it.

the wires are likely shot and are encased in insulation, very hard to peel. and you need to replace the entire length, should you want to. never done it, just heard it might be possible.

a new motor does not need to be programmed. replaced a bunch. good luck, chuck.

Similar problem with my '94 E320t was cured by new spark plug wires and coils.

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Robert Fini

'12 ML350 BlueTec, 100k
'06 E320CDI (x2)
'05 T1N Sprinter 2500/Pleasure-Way Plateau TS, 70k
'97 C36AMG, 319k (son's)
'94 E320T, 249k
'93 190E Sportline LE, 168k (daughter's)
'84 190E-2.3/5spd (Stage Rally Racer)
'66 230 W110 Sedan (Barn Find, Vintage Racer build in progress)