1991 230GE lumpy idle
I have a 1991 230GE with an LPG conversion. Had a problem with cold starting recently after the weather got a bit colder and discovered that the cold start valve was not spraying petrol at all. Traced this back to a blown fuse on a relay. Replaced fuse. This remedied the cold start valve, which then gave the required spray of petrol when starting from cold. However, having replaced this fuse, the idle became lumpy - I then realised that this unidentified relay must be controlling various other things besides the cold start valve, as when I switched on the air conditioning, the idle speed was increased too - this used to happen, but I'd noticed over the summer that switching on the aircon caused a lowering of idle speed, but didn't bother to look into it then as it didn't really cause major problems. What I want to know is what is that relay controlling, as it can't just be related to the Jetronic fuel injection system, as the lumpy idle happens when running on LPG the same as when running on petrol, if I remove the fuse once the engine's started it runs absolutely smooth....... Any ideas?
Would you post a photo and give the part number of the relay in question?
Wondering if the fuse was blown throughout the summer? You have mentioned the a/con did not increase its idle speed when engaged then; now the weather is turning cold you have needed to look into the matter and finding the blown fuse you have remedied the cold start problem but in doing so should the temperature sender unit also be faulty, the vehicle could be runing under a wrong mixture (Over-richened) giving you a lumpy idle (exhaust smoke would be black).
The temperature sender unit to the ECU is not the same as for the one to the gauge.
Does the lumpy idle even out when the engine warms up?
Cheers,
Sounds like the Auxilary Air Valve, see section 15.1.12:
http://www.auto-solve.com/mech_inj.htm
Symtoms will be worse on LPG as it is more sensative to air leaks (which is effectivly what this valve does). You can clean it with carb cleaner which can be bought from any motor factor. They get clogged with carbon and soot.
Russ
When you originally posted your thread, it seemed evident that your complaint could be weather related, hence the manifestation of your idle problem.
It seems now, that your idle problem is no longer temperature as related to weather. Therefore, it would be prudent to start with the basic checks.
You have not mentioned your engine type, there are two types of engines used on 230 GE's. Om 115 and OM 102, the former has adjustable valves and the latter has hydraulic valves (tappets).
If you have the OM 115 engine, do have the valve clearances checked and adjusted as necessary on a cold engine, preferably.
Should the garage you use, have the necessary diagnostic or engine tuning gear, they could test the engine condition on the diagnostic equipment, but remember, garages having the equipment, does not necessarily equate to them having the skill or experience to interpreted the results!
Having the skills, they should be able to tell you the engine condition by testing compression electronically by cancelling each cylinder's sparking individually and comparing the drop in revs for each cylinder and comparing the drop in engine revs. With each cylinder canceled out, they can also tell from the emissions analysis if a valve is burnt or has poor seating etc, etc...
Otherwise, they can use a conventional compression tester and check each cylinders compression. This test will immediately highlight any mechanical problems that might be.
They should be checking for any false air leaks in any and all rubber parts of the induction system. Start with the idle adjusting screw and follow the rubber plumbing connect to it. Get them to check the engine crank case breathing, there is usually a connection pipe between the rocker cover and the air filter housing, is the engine venting and gasing from the rocker cover into the air filter housing?
By the way, the engine revs you have mentioned in your latter thread should read in its hundredths, not thousands; you have mentioned figures of 5000 to 9000 and 7000 and 8000 rpm, they are infact 500-900 and 700-800 rpm. If there are no false air leaks present then consider having the throttle body's - butterfly valve edges cleaned off all built up carbon with brake or carbon cleaner.
This element of work does involve the dismantling of the injector body to get to the throttle body. Do not omit the cleaning of the idle control valve, if fitted; have that cleaned with brake or carbon cleaner. After all this get the timing re-checked and emission reset as necessary.
Then report back.
Good luck,
Suzie In your original post you mentioned that the cold start problem was due to a blown fuse on a relay. This is the over voltage protection relay (OVP) which as you have worked out controls various systems on the G. It is the only relay with a fuse on the top of it so it is easy to spot (see picture).
You state that when you remove the OVP after you have started the vehicle the idle speed stops fluctuating this would lead me to suspect the OVP is probably faulty. This is a common problem with this part and difficult to diagnose.
A new OVP is around £70 so it would be worth borrowing a working relay from another Mercedes G or saloon to test this theory first.
Hope this helps.
Thanks to everyone for your helpful replies.
Car booked in next week, Thursday, with my mechanic. I've forwarded all this info to him - let's hope he can get to the bottom of it this time. A couple of months ago, he stripped the top end of the engine, head went away for skimming, valve reseating etc, he reassembled it, set it up and it was lovely - it ran so smoothly, you could hardly hear it ticking over. Then the weather got a bit colder and the cold start issue became apparent. He traced it to the blown fuse - replaced that, then the tuning went off, he readjusted the mixture etc and the rest is what's you've been posting comments on.
Thanks again for all your help - I'll report back early the week after next, when I have it back, hopefully running beautifully again......
Hello suzierobs,
One 'nosey parker' eager to learn the out come of your idle problem with the last visit to the mechanic, what's the gossip? - please...
Regards,
Unfortunately I still have the same problem, as we ran into more pressing troubles with an MOT failure. Failed on some rust and a front wheel bearing - rot not too bad as managed to source a panel from Mercman in Cornwall. Bearing a nightmare - mechanic ordered kit and stripped old bearing out - fitted new bearings, all ok, but seals wrong size. Couldn't get the right ones anywhere - finally got them from Mercedes - should have tried there first, but when searching posts on here about wheel bearings, someone said Merc no longer do them, stupidly I believed that and didn't check - however, they do and they got them in next day for me, after waiting a week for other suppliers not to be able to source the right ones............
So, I now still have the lumpy idle and it will have to wait another little while to be looked into, as I'm driving up to the Lake District for Christmas on Wednesday.
I will post my news when I have some more to tell.....
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Thanks for your reply Rakesh. I've asked my mechanic to identify which relay needed the fuse replacing and will post again as soon as I hear back from him.
The lumpy idle doesn't even out once the engine's warm, it's always erratic, exhaust smoke not black though. Mechanic has adjusted the mixture and idle speed, but it's still erratic, doesn't matter if it's just started first thing from cold or whether it's fully warmed up. Idle is even more erratic on LPG than on petrol and can waver up and down between around 5000 rpm to 9000 rpm when first coming off the accelerator , although after giving it a few moments to settle into idle it will stick to wavering between 7000-8000 rpm