Engine stumble

[KermitF]

Hey guys,

I have a 1990 300E that has developed a curious problem.

After driving at high speed on interstate and pulling off onto surface street, the first time I have to make a stop (at light, stop sign, intersection w/yield sign, etc., the engine will idle smoothly for about 5-10 seconds then "stumble" twice, then, after another 3-5 seconds, "Stumble" one more time - usuually in this same pattern. Plugs are new and right kind, coil is new, OVP is new.
This problem has happened both before and after these items replaced.

Anyone experienced anything like this w/their car?

[cjlipps]

Do a search on the forum for more ideas but mine was the cap and rotor.

[gmercoleza]

Pop the hood at night in a very dark location, perhaps unlit garage (with the door open of course). Look for any arcing of spark around the cap and coil, but especially along the ignition wire. Spray an ultra-fine mist of water along these areas to see if doing to creates any arcing. If you get lots of arcing, replace your wires. As noted earlier, the cap and rotor are also usual suspects.

[KermitF]

Replaced cap & rotor at 160K mi.

Car currently has 205K mi.

Cap, rotor should not have died after only 45K mi., should they?

[gmercoleza]

Originally Posted by KermitF

Cap, rotor should not have died after only 45K mi., should they?

They should not have, but it does happen. And as pointed out earlier, check for arcing on your wires.

[brandob9]

I have the same problem on my '86 300E, but my wires, cap and rotor are new in the last 5,000 miles.

[david s poole]

you probably need fuel distributor.

[zcc]

Also check the fuel pump relay.

[KermitF]

OK guys,

I did see arcing of wires when started in dark garage and wires sprayed w/mist. Wire to coil, and at least one plug wire glowed.

Sounds like my next step is to replace wires.

What kind/manufacturer is best?

[just-n-time]

After you replace wires and you are sure the cap and rotor is good,If the drop in Idle is still with you, The potentiometer would be the culprit,This device keeps the engine from dipping to low on deceleration.

[KermitF]

(Updated to clarify that coil wire - not coil - replaced.)

OK guys,

Have installed new Beru wires plugs and coil wire.

About a week now and problem has not yet recurred.

I have not yet replicated all conditions where problem seemed to arise, but so far, so good.

Will update after doing interstate drive next week.

Thx for all assistance to date.

[KermitF]

After traveling 1,200 miles to and from Indianapolis (to see McLaren-Mercedes finish one-two in the US Grand Prix this past weekend), I can confirm that the plug wires solved my engine stumble problem. Thx again to all who gave me advice.