W124/E320 Coupe hesitation and wobbly idle

[W124coupe]

Hi all, I have a 1995 E320 coupe, UK spec (so cable throttle and no LED/push switch and nothing on port 14 etc), 105k miles.

I have a couple of problems which I hope you can help me with (possibly related?)!

The car has a wobbly idle when hot - RPMs stay at about 600 but irrelgular "beat" to the idle which can be heard through the exhaust and also "wobble" the car.

Accelerating fairly quickly, the car has a flat spot/stumbles 3-3,500 RPM and then "takes off" at around 4,000 RPM - feels like my wife's VW turbodiesel hitting the turbo...makes the car feel unresponsive around 70/80 in 4th on the motorway.

Also, shift from 2->3 snatches a bit although 3->4 is smooth - seems to need a lot of throttle (even on a steep hill) to make the box drop 4->3 - can't see any vacuum pipe issues but there's a whole lot of pipes!

Haven't yet cleaned out the EGR port (no fault code to indicate I need to?).

Wiring harness is new (2 years) and the insulation on the coil feeds is clean and supple. PO supplied invoice showing 3 x new coils last year plus an ECU recon ("output stage blown by faulty coil" according to the invoice).

The car is new to me and sat for over a year as its PO was ill.

I have done the full B service as per the book plus trans fluid and filter, correct new Bosch plugs and resistor caps, cleaned the (filthy) throttle butterfly, checked MAF (clean), cleaned the intake temp sensor (filthy).

I also sat and cleaned up the fuse box connectors and fitted all new fuses (the old ones were corroded).

OVP is part number 000 540 67 45. No rattles and solder inside clean and shiny, checked the gap - clean (also no ABS light except at switch-on).

Reading codes, there is just one on pin 8 - code 32 (which I can't find listed).

What should I check/do next?

[kth286]

Steve

Code 32 is one of the two knock sensors and/or circuit.

I suspect the harness plug/s has not been snapped into the locked position on one or the two knock sensors due to difficulty with access under the inlet manifold.
The ignition is probably being retarded by the ECU as a result of the open circuit.

I doubt your car has EGR as my UK spec E320 Coupe 1995 does not.

Regards

[W124coupe]

Hi, thanks for that - 2 questions please:

Can you describe where the knock sensors and connector are?

Can you point me at the error code list that you used (the ones I found by searching stop at 28)?

Thanks,

[kth286]

Steve

The two sensors are fixed to the block under the inlet manifold.

If I remember correctly, I had to reach up from underneath the front nearside of the car (front wheel off) to refit the two plugs onto the knock sensors, when I replaced my wiring loom.

The plugs on the end of the wires will likely just be resting on the sensors I guess (if that is indeed the problem).

Where in the UK are you - I am in Berks - possible to meet up ?

Regards

David williams

[W124coupe]

Hi, I'm near Redditch in the Midlands.

Do you have a list of the (pin 8) codes for this car?

I thought I had found them but the list I have stops at 28 and lists 25 as the code for the knock sensors....

[W124coupe]

Well I found the knock sensors and the fittings were on and tight (they have clips holding them on). I unclipped the front one and the connectors are clean and bright. Looking at the rear one it is tight and clipped so I didn't disturb it.

Their wires disappear into the main loom without a connector so I can't check any further - not sure what to do next?

[W124coupe]

OK, no replies so here's what I'm going to do:

Knock sensor wiring doesn't seem to go to the ECU via any connectors except the clip on obnes at the sensor bodies so I will take off the ECU connector and check the cable continuity for ground and signal to the two sensors:

From a PDF I found, ECU plug B pin 40 is sensor 1 ground, 41 sensor 1 signal, 42 sensor 2 ground and 43 sensor 2 signal.

Assuming these check out OK for continuity, I will then buy one sensor and check by substitution if the code 32 and symptoms go away.

(as far as I can see, the sensor wire runs are not protected by any RFI screen so nothing to check/ground there??)



Anyone see any issues with this as a plan?

[kth286]

Steve

Have you tried clearing that code anyway ? What happens ?

Regards

[W124coupe]

Clears and than comes back after a couple of journeys.

Still hesistant accelerating and 20MPG on a recent 200 mile/80MPH trip.

Waiting for a big storm to end to try the ECU/continuity test of the wiring.

[W124coupe]

OK, fixed it!

The rear sensor cable had been pinched at some time and was shorted out. ECU must have been reading zero.

Had to make a tool from a barbecue fork to get the connector off and back on as I couldn't see any way to get a hand in there but managed to strip and repair the flylead with some high temp self-amalgamating tape.

No more flat spot and no more pin8 codes!

[kth286]

Steve

Well done - very satisfying isn't it.

Regards