Diagnosing an intermittent D-Jet problem..., Hesitation under load at 2800 RPM but only when cold... Options

[MikeInMunich]

Hi again from Munich!

Here are the details. But please see update from Feb. 5th below!

I have a D-Jetronic intake. Under load and at about 2800 RPM Im experiencing an intermittent hesitation. Yesterday my son and I took the car out for a drive from Munich, towards Innsbruck and back and we ran into a bit of rain coming along the Aachensee (lake), and this hesitation got worse. Then I remembered the only other time I've had this car out with 100% humidity and that it wasn't running well on that day either, so this is apparently a clue.

So what can this be? And why does it happen at all, even when it's not raining, albeit not as noticeably? Is there a cure?

Experts / senior gurus out there, thank you for your time and sharing your knowledge and experience, in advance!

With kind regards,

Mike in Munich
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[Dave_Darling]

The "AT idle" is determined by the idle contacts in the throttle position switch. If they are closed, the knob will have a small effect on the mixture. If those contacts are not closed, the knob should have no effect.

--DD

[MikeInMunich]

Hi Dave,

thanks for chiming in again here. I've read through Brad's work on Rennlist at least 5 times over the past few months and am at it again. I currently have FIVE AAR valves here, at least three of which I've had an employee (bike mechanic) of mine open up and clean / restore. It seems like none of them are open when cold. The car idles, somewhat roughly but not stalling, around 1000 RPM but not where it belongs, like at 1600. According to Brad on Rennlist, iirc, the extra air has no effect on the idle speed if the mixture is too lean. So my next test will be to turn the knob on the ECU all the way clockwise and see if the car 1) idles higher when cold and 2) if the hesitation is lessened.

Since the CHTS has to do with heat, resistance and mixture, and the problem is going away almost entirely when the engine is fully warm, im thinking it has to do with the mixture and the CHTS. I'm also checking tomorrow if this sensor is actually the one that belongs with the ECU I have. One of them has a Resistance of just 1100 Ohms at ambient temperature and another is well over 2000. I've got the one that's over 2k but I'm not sure at the moment if that's the one that belongs with this system.

I will continue to update until this issue is solved!

Brad, if you're reading this, thanks for all your info. Your sheet on the D Jetronic on Rennlist is legendary. By the way, this 1.7 engine was expanded to 1996 cc or whatever, just under 2ltr. The cam is stock. Ignition is electronic. Fuel pressure is 29 psi. Injectors, wires, plugs, all new. I will check the grounds and use the Ohm meter here and there and report back again.

Thanks gentlemen.

M.i.M.