w124uk

Hi guys!
I'm really desperate to solve the uneven idle when engine gets warm. Thought it might be the oxygen sensor, replaced but no luck. Just to let you know I've checked (and/or replaced the following):
Spark plugs (new)
HT leads (new)
distributor cap
rotor arm
fuel filter (new)
lamba sond = oxygen sensor (new)
chekced the injector seals
injector cleaner (3 bottles)
OVP relay
and probably a couple of other minor things

Now I'm running out of ideas...could it be the ECU? I had no idea the car can actually run with the ecu disconnected (runs rougher than usual but I did have it running with the disconnected Jetronic ECU in my hand!). Do you know if the ECU is likely to pack up?
Hope to get it fixed....hope you can help! I do like the car and want it fixed once and for all!

Parshman

check to see if you have a hole in one of the spark plug caps to see if the electric is arcing out which could cause that.

w124uk

No way, spark plug leads (HT leads) are brand new quality parts.... and checked the car in the dark, even sprayed some water to see if it sparks...

shadowgriffen

I take it you've check/replaced the OVP relay/fuse?

w124uk

Yes. It's been done as well

shadowgriffen

You state you have "new" plugs...have you by any chance replaced the Factory recomended coppers to Platinums?

If so, that may the culprit.

w124uk

Just standard NGK spark plugs (never had ANY problems with NGK/NTK products) with the correct gaps of course... so I'm afraid it's not the culprit :-( running out of ideas...

My next guess ie seither the ECU or Air mass meter + fuel distributor + throttle body combo..... or maybe the temperature sensor...what do you think?

shdoug

From what I know about K-Jet systems in general, the ECU basically modifies the air/fuel mixture using the readings from the Oxygen Sensor and probably some other inputs. It is strictly for emission control, or so it was on my cars with K-jet (the latest of which was a 1985 Volvo Turbo). It is a fairly simple, electro-mechanical (as opposed to electronic) system. If it runs rough without the ECU, look for :

1. Vacuum leak, leaks at idle control valve hose- most likely
2. Intake manifold gasket leak (another form of vacuum leak)
3. Is it a rhythmic miss, as in just one cylinder not firing at idle? if so:
A. determine which cylinder it is by disconnecting spark plug leads until you find the one with the least change.
B. Double-check the obvious, like the plug and wire.
C. Spray WD-40 around the intake in that area, including injector seal (I don't know if you checked them this way or some other, but this works)
D. Swap the injector with another and see if the miss follows. If so, replace the injector.
2. Mixture too lean (not enough fuel) There should be an adjustment for this but don't screw with it until you've checked everything else. Remember where the adjusment screw was so you can put it back if necessary.

My Volvo had this problem and it was a bad intake manifold gasket. The turbo boost had blown one of the rings around a cylinder. I wouldn't think this would happen on a non-turbo engine, but who knows.

Good Luck!

bjay51d

Check the inside of you distributer cap.Sometimes theres a green build up that forms.I just scraped that build up off of mine which hepled idle abit.I read somewhere that youre suppose to change the o rings inside the cap. Which I didnt, I just reused the old one.So i think I will order a new cap.And do it right , clean that oily film out and replace the o rings.

w124uk

Well, the dizzy cap and rotor arm were OK...it's not an ignition-related problem, it's fuel supply / air supply related :-(

shdoug

So, did you try the misfire test? Is it like a misfire or just "uneven"? Does that mean it goes up and down like it's hunting?

tokleman yanass

The ECU is not likely to be defective - can happen but not frequent. Your problem sounds not unlike mine - except mine goes away. If the car runs ok cold but starts running rough when it warms up I suspect the temp sensor (amongst many other possibilities) - you could try removing the wires and crossing them - the ecu gets a low resistance signal from the sensor when it gets up to running temp and adjusts the mix accordingly. Or you could test the resistance from the sensor - i think about 6kohm cold, 300-400ohm warm.
Bon chance.

w124uk

It's not a regular missfire - the revvs are not going up and down, it's just running "rough" and the engine shakes....

w124uk

It was one of the things I was trying to check..but my temperature sensor has 4 wires going to it...and I have no clue how to check it...HELP!

tokleman yanass

theres a temp sender for the gauge in the dash, and another one at the very back of the head for the ecu - are you sure you're checking the right one?

shdoug

Then it almost has to be a vacuum leak (manifold, idle control valve hose, manifold vacuum tap, etc) OR improper fuel mixture. Remember, all the ECU does is MODIFY the fuel mixture; it's not a complicated magic box. To check the mixture, move the Air Flow Sensor (I'm assuming this is accessible from underneath the air cleaner housing) toward the open position, slightly at first, while it is running rough and see how it affects the idle. If it improves, it's too lean. If it gets worse, try moving it toward the closed position. If that improves the idle, it's too rich. If it is a mixture probelm, move on to the temp sensor and things the other people mentioned. The goal is to find out if it's a mechanical or electrical (sensor) problem first. Remember, it's a simple, electro-mechanical system; it should be fairly easy to pinpoint the problem. Research Bosch K-Jetronic on the net to see how it works, or read some of my posts which have some more details. You'll figure it out very soon, just hang in there!

BTW, I've read here that achieving a smooth idle on the M103 engine is alsost impossible, but I don't know why it should be.

tokleman yanass

yeah, vacuum hoses can cause chaos - the one at the back of the engine that goes to the tranny has a habit of coming out causing rough running and erratic gearshifting - my mechanic pointed that one out to me the first time i saw him cos he gets sick of people getting their cars towed in for a fix that takes 15 seconds...

w124uk

Hope it's not true, I'm used to smooth idle, especially on 6 cyl engines.
Guess you may be right...I've ordered the temp sensor just in case (it's only $40). I guess during the previous service (almost a year ago when it all started) the garage may have tried to adjust the mixture (looks like the tamper-proof plug is missing from the mixture adjustment on the throttle body). I'll have to put it on an ehxaust gas analyser and see if I can fix it anyhow... I managed to locate a throttle body / air mass meter / fuel distributor unit from a working 260E fot $160 so it may also be an option...

w124uk

Sounds interesting, over the weekend I'll try to gat it in the workshop and check the hose in question... I've got some stuff planned for the weekend already - want to replace the tranny fluid and filter, need to replace the ribbed belt because it's getting old and cracked. When I'm at replacing the ATF in the gearbox, I'll replace he ATF in the power steering system and the power steering filter as well.

de_dust

Have you checked the coolant temp sensor?

ptoro01

atf in power steering is a bad idea mister. Your lovely vehicle takes power steering fluid.
My m103 is running dead smooth but idles a little low. Few things I did... Injector seals are a must, check for brittle vacuum lines and especially the connectors. The idle control valve has 2 big rubber hoses coming out of it, replace those, that made the biggest difference and while doing so, flush your idle control valve with throttle cleaner(black gooo will come out of it for sure).

You said your engine was shaking, often if a motor mount goes flat, the engine will shake like a seizure. If you have a sticky injector, that will also shake the engine like crazy. Another issue could be that you have loose rocker arms and a cam going flat, check for that.

tokleman yanass

if the mixture screw covers been removed - uh oh...when i got my car some moron had actually busted the mixture screw housing f..ing around with the mix - i had to get a whole new casing fitted