190E engine speeding up and down on overrun- air flow pot?

[carrington]

hi. new to me... 1993 190E 2.0, as title. seems to rev up and down a little on the overrun, coasting. adjusted the throttle cable and linkage better and tested the deceleration microswitch. seems good. going to test the potentiometer tomorrow hopefully as this seems to be the only cause i can find to match the symptoms now? car seems a little rich and fuel consumption is poor. will be checking cold start valve for leaks as well, just in case that's leaking though. or as well...

Any better informed ideas, experiences to share?
Cheers

 

[carrington]

well a few basic tests passed, did notice the air flow pressure plate was a bit sticky, good clean ensued but i'm sure i've read the plate is supposed to be set up flush with the top of the venturi tube and mine is 2 or 3mm down from there - that would make it run rich, right?

 

[grober]

http://www.berlinasportivo.com/Technical/lancia/Thema832/Bosch-KE-Jetronic-OCR.pdf
SOMEONE COULD HAVE FIDDLED WITH THE IDLE ADUSTMENT SCREW [7 ON MAIN DIAGRAM]------THIS IS INCREDIBLY SENSITIVE AND SHOULD ONLY BE ADJUSTED WITH AN EXHAUST GAS ANALYSER TO MEASURE THE AIR/FUEL RATIO FROM THEE EXHAUST.
OTHER PROBLEM MIGHT BE WITH THE ELECTRICAL THROTTLE VALVE SWITCH[13 0N MAIN DIAGRAM] WHICH SIGNALS END POSITIONS OF THROTTLE PLATE---FULLY OPEN/FULLY CLOSED ----SEE PAGE 21

 

[carrington]

nivc link, that will be useful.

well it's in the shop tomorrow for adjustment, going to get them to look at throttle linkage as well so fingers crossed

 

[carrington]

reading around, looks like the problem on the over run might be caused by faulty speed sensor, haven't worked out if TPS or road speed sensor in the binnacle, so need to test those. once it stops snowing.

 

[ray_hennig]

well it's in the shop tomorrow

Good luck. I hope the "shop" has some old school staff that understand these cars. An increasingly rare qualification these days.

RayH

 

[carrington]

seems to have got worse in the last ten years or so, getting hard to find anyone who wants to do it. oh well it's not exactly rocket surgery, i'll probably get it sorted eventually

 

[190]

Unlike my 1989 190e, yours is closed loop control with a cat and lambda sensor so my experience will have been different. On mine the overrun microswitch cut the fuel flow completely provided the engine was above a certain number of revs . I could actually feel it happening while driving.

I did have trouble with the cold start valve, although not the valve itself which didn't leak. It was the ECU telling the valve to open when it shouldn't have been. I ended up pulling the plug on it so it could be eliminated as a problem and the car still started fine. I suspect it was only supposed to operate in really cold temperatures. Might be worth a try.

The cold start valve squirts fuel into one end of the manifold and if it's operating when it shouldn't there could be a pool of fuel there the whole time.

Bosch K was a nice simple mechanical fuel injection system that worked well. I think they made it potentially less reliable when the electronics were added to make it the Ke system.

 

[carrington]

Unlike my 1989 190e, yours is closed loop control with a cat and lambda sensor so my experience will have been different. On mine the overrun microswitch cut the fuel flow completely provided the engine was above a certain number of revs . I could actually feel it happening while driving.

I did have trouble with the cold start valve, although not the valve itself which didn't leak. It was the ECU telling the valve to open when it shouldn't have been. I ended up pulling the plug on it so it could be eliminated as a problem and the car still started fine. I suspect it was only supposed to operate in really cold temperatures. Might be worth a try.

The cold start valve squirts fuel into one end of the manifold and if it's operating when it shouldn't there could be a pool of fuel there the whole time.

Bosch K was a nice simple mechanical fuel injection system that worked well. I think they made it potentially less reliable when the electronics were added to make it the Ke system.

hi yes my old 230TE was a lot simpler to work on. It's basically the same system with a few extra bits literally bolted on as far as I can see. I just discovered that the deceleration phase uses a road speed signal from a Hall sensor on the speedo cable - and my speedo is twitchy at low speed... and also has some electrical problem with the dash light potentiometer, it sometimes goes out and need a tap to bring it back on, also the fuel gauge is sticky sometimes. not sure how relevant it all is but i need to test the hall speed sensor and pull out the binnacle and have a good look round.
have tested the cold start valve, seems to be working ok and not leaking, the decel microswitch seems to be working - had to adjust the throttle cable and clean up layers of burned on crud on the linkage track and roller and greased up with something that set hard a long time ago... seems happier now at least. Also need to check the TPS i think. I found some MB sheets that mention testing the road speed sensor for revs varying on the overrun so i'll keep down that rabbit hole for a bit. cheers!