Throttle revs up by itself...

[CrimsonBrian]

Hey gurus!
I have been having this problem for a little while now and it seems totally unaffected by weather, the A/C or how long the car has been running. What happens is that when I take my foot off the gas or put in the clutch to stop or change gears, the car reacts as if I have jammed on the gas. It will climb all the way to redline unless I lightly tap the gas in which case it goes back to normal. The car seems to want to accellarate on its own and, needless to say, this is bad. I have no idea what it could be. I have checked where the pedal meets the floor to make sure nothing is caught but that hasnt helped at all. Any ideas? I want to have an idea of what is going on before I have my indy or the stealer give it the once over. Thanks!

Brian

[stu1]

I guess the first thing to find out is whether the throttle is actually open or not. The next time it does it, just switch it off then remove the air intake pipe from the throttle plate to see whether it's open or not. I'd also check it was mechanically sound as well.

If not it's probably your Idle Control Valve jammed/sticking open.

Best,
Stu.

[CrimsonBrian]

Thanks Stu! Although, I have to admit that I wouldnt know the first thing about doing that, I am a total mechanical idiot. Is there some way to grease the idle control valve? Should I just have it replaced? Thanks!

[Kalevera]

ICV.

It's a pain in the ass to get to on the M50 -- underneath the intake. The three lead kind on your car can't be cleaned without destroying it; it needs to be replaced. Also, when you change the ICV, the DME has to be reset, otherwise it will likely work the new ICV as it did the old/malfunctioning unit, and there'll be no noticeable improvement in the problem.

best, whit

[CheapCheap1]

that the ICV will be automatically cleaned, when the rpm is over 3,000???

[Beemr750]

Check or adjust throttle switch

[CrimsonBrian]

Thanks everyone, I'll pull out my Bentley and see if I can figure out where all these items are. Then I will take it to the shop and see what they say. Is all of this going to set me back a bazillion dollars?

[Kalevera]

Hmmm -- once the three lead ICV gets clogged, it's only fit for the trash. The actuator spinning might remove some of the nasty residue that collects on these things and send it down the intake; whatever internal cleaning controls may exist don't guarantee a reliable or consistent lifespan.

best, whit

[ryan roopnarine]

i know this differs from what everyone else says....

i think that your cruise control cable may be falling off, pulling the throttle open when you aren't pushing on the accelerator. there's a safety campaign part for it, if it isn't on properly this may happen. either this, or the throttle position sensor may be going flaky.

lowell....what do you mean when you say you can't clean the three lead icv without destroying it?

[Kalevera]

IIRC, a new ICV is something like $150. It could be another component, but it'd be the first thing that I would check.

best, whit

[Kalevera]

i know this differs from what everyone else says....

i think that your cruise control cable may be falling off, pulling the throttle open when you aren't pushing on the accelerator. there's a safety campaign part for it, if it isn't on properly this may happen. either this, or the throttle position sensor may be going flaky.

lowell....what do you mean when you say you can't clean the three lead icv without destroying it?
The only serviceable ICV is the two lead (read: early) units found in 80's cars. By the end of the decade, everything used the three lead version; said unit has seals between the mechanism and the electrics that are sensitive to cleaning agents and solvents. Taking a can of brake/carb cleaner will kill the unit within a few operational minutes. Happens all the time -- I replace a lot of ICVs these days.

best, whit

[CrimsonBrian]

Whit,
Are you a mechanic? And are you anywhere near Boston?

[Bellicose Right Winger]

Ryan is correct. There was a recall campaign to correct this problem. The plastic end of the throttle or cruise cable breaks near the throttle body, often due to a ham-fisted mechanic working on M50 in vicinity of fuel lines or brake booster. The recall installs two spring clips to keep the plastic ends together and prevent throttle from staying open. If you can open the hood you can inspect these cables.

Paul Shovestul

[CrimsonBrian]

Ryan is correct. There was a recall campaign to correct this problem. The plastic end of the throttle or cruise cable breaks near the throttle body, often due to a ham-fisted mechanic working on M50 in vicinity of fuel lines or brake booster. The recall installs two spring clips to keep the plastic ends together and prevent throttle from staying open. If you can open the hood you can inspect these cables.

Paul Shovestul

OK, so I should open the hood and then what should I look for? I'm sorry to pepper you guys with such novice questions, but this is out of my area of expertise. Also, if this was a recall, is this something the dealer will fix for me?

Brian

[Bellicose Right Winger]

Open hood, use Bentley to find throttle body, have helper step on gas pedal repeatedly until you detect motion at throttle body. Closely inspect two cables attached to throttle body. Next time throttle jams, use Stu1's procedure and inspect cables again. Need to rule out simple causes before moving to expensive ICV fixes. Yes, dealer should install clips for free, but they won't replace the broken cables.

Paul Shovestul




OK, so I should open the hood and then what should I look for? I'm sorry to pepper you guys with such novice questions, but this is out of my area of expertise. Also, if this was a recall, is this something the dealer will fix for me?

Brian

[632 Regal]

HEY! no such thing as a novice question here...usually we like to help. Im not sure where the cable runs on a 525.

[stu1]

I'm no expert so treat all of this with a large grain of salt; but the following worked for me.


Yes, as Paul Shovestul said, open the bonnet and have someone prode the accelerator/gas pedal. You'll see the throttle cable moving the throttle. Connected to the throttle housing will be a large air pipe; this is connected to the Mass Airflow Meter (MAF) and in front of that will be the air filter box.

The large air pipe is connected to the throttle housing by a large jubilee clip; if you loosen this, the pipe will pull off (maybe with a bit of a struggle). Now you can see the actual throttle valve (or plate) - this should move freely; if not that's your problem.

However, as others have noted the most likely culprit is the idle control valve (ICV). When the car is at idle, the throttle is fully closed; no air can get by it, so the ICV allows a small amount of air past the throttle plate. It needs to vary to take account of varying loads on the engine whilst at idle; for instance Air Con. The way it works is via an electromagnet which can either be on or off. If the electromagnet is on the valve gets pulled one way and if off, the valve is pushed the other way. The way it is fully controlled is by varying the ratio of on to off pulses; for instance if in 1 tenth of a second the power is applied for half that time then the valve will be half open. If the power is applied for 90% of that 1 tenth of a second the the valve will be 90% open. (The actual pulse rate; I've used a tenth of a second here, or 10Hertz, is dependent on the mass of the actual valve). Anyway, I believe the ICV on the M50 is controlled by a seperate controller ((and not the main DME, or ECU as it's known on other cars) - I'm happy to be corrected on this :)). Anyway, I know others have said you can't clean the ICV on later models, but mine's a 94 and I succesfully cleaned mine up - here's how.

On the large rubber air intake pipe, right before it connects to the throttle housing, you'll find a small tube coming off the bottom of it; this is the air feed to the ICV. Get a bottle of Redex, and with the engine running at a fast idle, slowly empty the whole bottle into the small tube leading to the ICV; it's also well worth getting some into the main throttle body as well. Very little will happen, but just let the whole bottle go in. Now switch off the engine and leave it for a few minutes; then start the engine back up (you may need some gas to get it going, and it may not idle) take it for a damn good thrash around some fast roads.

At this point a warning is in order - there will be a great deal of smoke out of the exhaust - this is the redex getting burnt off. And we're not talking small amounts here; we're talking huge amounts of really embarrassing grey smoke. Doing this out in the countryside is good :)

Anyway, that completely cured my rough idle and my ICV is still fine - smooth as silk now; fantastic in crawling traffic; it even drives itself up and down gradients at a nice constant speed.

Might be worth a try; besides if your ICV has moved onto BMW heaven, well it was knackered anyway.

Stu.

[stu1]

Oh, a quick note; the car probably won't idle with the air intake pipe disconnected from the throttle housing; if this is the case, if I remember right, disconnecting the electrical plug from the MAF will allow it to idle.

Best,
Stu.