Idle Control Valve
 

Question...

Is it common to replace the idle control valve on a '86 300E?? The car runs great, but sometimes it seems to idle rough, and on occassion will even stall out when the car is in gear - stopped or just crawling along very slowly.

When the weather is cold - this is never a problem. Any thoughts???

Paul

I was told to try cleaning it with a cleaner, then spray a little WD-40... didn't seem to work.

Is there a way to test before replacing it??

I can't speak to whether or not that's your problem, but the idle valve is a fairly popular item.

Ron
http://germanstar.net

I have battled with this exact problem for several months. It generally occurs just after the engine hits operating temperature.

The advice that I have gotten has been that the ECU is telling the idle valve to shut down because of bogus inputs. The usual suspects are the air flow meter, throttle position sensor, and decel micro switch. Vacuum leaks are also suspects.

Problems with the valve itself seem to be idle speed high or low or surging.

The only clue that I have gotten was when it failed when I had a meter connected to the EHA test harness. The EHA current went to +2 - +4 mA when it happened as opposed to swinging around 0 at very low levels when it was running well.

I can tell you what I have done that has not fixed the problem:

- plug wires have 15K miles on them
- checked for vacuum leaks
- cleaned rotor and cap
- new Bosch HD9C plugs
- new OVP relay
- new air flow meter
- new O2 sensor and lambda adjustment
- new coil
- checked decel and throttle switches

All of the replacements have made the car run better, the air flow meter especially. I put the coil in last night, and now when it goes rough it does not die.

I am going to do a post on this with more detail on the latest developments and see what the experts say.

Chuck, I'd recheck the OVP. The new one I installed temporarily cleared up low idle and stalling, then the problem started returning. I disassembled it and resoldered the board contacts, and no problems in months since.

The issue seems to occur because of an assembly line problem. The internal solder pins are clipped back AFTER soldering, and I think the stress of the clipping physically damages the solder joint integrity. Eventually, the bad contact causes pitting, and operation is erratic. I have seen this in other electronics where this procedure is used.

Steve

I should have added that during last weekend's stumbling, I got an ABS light. So I replaced both the OVP and the coil (for good measure) last night. Is it conceivable I could have this problem on a new OVP?

Given the state of manufacturing today and the (lack of) quality control, I'd not bet ANY new part was either to spec or not defective.

Idle control valve induced stalling can be the OVP letting the supply current wobble or leaking control valve hoses. They get hard and shrink, then expand when warm and get loose on the valve, so you get intermittant large vac leaks. This will cause lean running as the air isn't going past the air flow sensor, the EHA current will go up as the o2 sensor sees lean condition, but you will probably stall due to the time lag on the O2 sensor at idle.

Check those hoses, and all the rest too -- a bad vac line will cause lean running and stalling problems at idle.

Peter

Peter -

That is the best theory anyone has come up with - thanks.

The only issue is that it is so intermittent that it fits with some flakely electronic piece rather than plain old vacuum. I will give it a try, though.

My current theory is that I have a flakey injector and am getting a lean misfire.

This is driving me nuts - BMW has new 3-Series for $299 a month lease which is starting to look good compared to $200 a month in parts to try to fix this elusive problem. My biggest fear is that I will drop another few hundred and then find out it's the ECU.

I had the same problem with the 300TE when I got it three years ago, fixed it with replacement of said hoses and all the vac line connectors.

Still have a rough idle, but that is the serpentine belt slipping and grabbing, going to fix that on Monday I hope.

Peter

Paul,

I had the exact same problems with my 84 380
SE. Replaced idle control valve, and problems disappeared.