W201 190E early - cold start hesitation - is it the temperature sensor or the warm-up regulator

Started by Boonie_W108, 08-07-2025 11:48 AM. 11 replies. 1,438 views.

08-07-2025 11:48 AM

Boonie_W108 Senior Member

Join Date: Feb 2014
Location: Marrickville NSW
Posts: 1,418
Club: M.A.L.A.K.A.S.
Car: '67 W108 250SE

BOYS

HELPING ANOTHER COUSIN. 1985 190E. M102 2.0. K-JET.

COLD START IS SHIT. CAR FIRES THEN STUMBLES FOR 30 SECONDS THEN RUNS FINE.

ONLY ON COLD MORNINGS. WARM ITS PERFECT.

IS IT THE TEMP SENSOR. THE WARM-UP REGULATOR. SOMETHING ELSE.

COUSIN HAS ALREADY REPLACED THE COLD START INJECTOR. NO CHANGE.

08-07-2025 12:48 PM

Vasilios_Billy

Lifetime Benzer

Join Date: Mar 2008
Location: Campbelltown NSW
Posts: 2,118
Club: M.A.L.A.K.A.S.
Car: 2020 AMG GT C

Boonie.. M102 K-Jet 190E, id go temp sensor first.

Engine coolant temperature sensor (the K-Jet one, not the gauge sender). sits in the cylinder head water gallery near the thermostat housing.. two-wire sensor with a specific resistance curve. If it fails open the K-Jet system reads "warm engine" and does not enrich on cold start. Test with a multimeter at 20 degrees: should read about 2,500-3,000 ohms. At 80 degrees: 280-340 ohms.

Warm-up regulator (WUR) line vacuum signal. check vacuum line cold. cracked or off and the WUR gets the wrong idea. enrichment goes wierd..

WUR itself. only after sensor and line. Bosch tester or send it out. dont throw parts at it.

Most likely temp sensor. about $65 retail and 5 minute change.

08-07-2025 02:18 PM

Boonie_W108 Senior Member

Join Date: Feb 2014
Location: Marrickville NSW
Posts: 1,418
Club: M.A.L.A.K.A.S.
Car: '67 W108 250SE

BILLY. WILL TEST THE TEMP SENSOR TONIGHT WITH HIM.

09-07-2025 09:48 AM

Boonie_W108 Senior Member

Join Date: Feb 2014
Location: Marrickville NSW
Posts: 1,418
Club: M.A.L.A.K.A.S.
Car: '67 W108 250SE

BILLY.

TEMP SENSOR. 480 OHMS AT 18 DEGREES SHOULD HAVE BEEN 2,800. SENSOR DEAD.

NEW ONE IN. CAR FIRES PERFECTLY ON THE FIRST COLD START THIS MORNING. COUSIN HAS HIS LIFE BACK

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