Author Topic: High idle, she won't come down. (Read 8822 times)

Sophia69IS · « **on:** September 09, 2012, 01:33:28 PM »

Hey folks,

I decided to write a new thread because I was unable to find what I was looking for on the other threads in this forum.

As the title suggests, my car is idling high and she won't come down, here are some facts to help weed things out.

I have just recently completed "the mess under the intake" after one of my heater coolant lines burst, I have replaced almost every coolant hose, everything has been put back together, as of right now, there isn't any air left in the coolant lines as I have bled it all out.

The Problem:

When the engine starts cold (starts fine, no problems) it idles a little low but then levels off and starts idling at the correct RPM's, a little below 1K, after a few minutes when the engine starts to heat up, the RPM's steadly rise and then stay around 1200RPM's and 1500RPM's I have no idea why it's idling so high.

I have checked all vacuum hoses for a possible leak, everything is secure, I have rechecked my ICV, looks good, the idle isn't fluctuating, it is just steady at a high RPM, NOTE: I did change the position of the ICV slightly.

I don't really have any ideas other than a vacuum leak which I have checked and re-checked for, everything seems to be hooked up correctly and she starts right up then starts idling high.

Any advice on this would be very much appreciated as this is my DD, and would like to get her back on the road this weekend.

Thanks so much for your help in advance!

Cheers!

Sophia from Seattle

ti_tony · « **Reply #1 on:** September 09, 2012, 06:23:22 PM »

Something you could check is the blue temp. sensor and the black temp.
sending unit since they are in the area. Maybe someone can confirm, the blue sensor will affect idle and should ohm out at 2500, it's in the front.
The black is a sending unit and not sure if it will affect idle. These are both on the drivers side of the head right under intake runners #1 & #2 .

DesktopDave · « **Reply #2 on:** September 09, 2012, 06:47:23 PM »

Yep, that temp sensor is a likely culprit. There are actually three on the earlier cars - one for the coolant temp to the engine computer (ECU, DME), one that just runs the gauge in the cluster, and a third in the AFM on pins 4&5. They change resistance based on temperature, and the computer uses that info to run the motor.

The connections are different depending on year too - the later cars have a single coolant temp sensor. Post your model in your signature so we can help out more.

Here's another quick think you can do - try the "stomp test." If you have a pre-96 car you can get the codes without a scanner. Put the key in the igntion, and turn it to position II but don't start the car. It's where the key would usually be sitting when the car is running. Once you've turned the key there, rapidly stomp the gas pedal to the floor five or six times within about ten seconds. It can be tricky to make this work. If you succeed, the DME will send trouble codes to the check engine light. You count the flashes and look up the code. Google it if I'm not being clear on this. Post your results (hopefully not 1444).

Sophia69IS · « **Reply #3 on:** September 09, 2012, 06:56:13 PM »

Thanks! Yeah, I think there are two sensors under there. The CEL light is not on, but I will try the stomp test.

Oh, the car is a 1991 318is

colin86325 · « **Reply #4 on:** September 10, 2012, 07:12:10 AM »

Does the ICV buzz/hum when the ignition is on and the engine is not running?

Sophia69IS · « **Reply #5 on:** September 28, 2012, 09:37:02 PM »

Thanks for everyone's replies, sorry it took me awhile to update, I have been really busy and biking to work since this car is my DD.

I have gotten new vacuum lines and tried the brake kleen thing, AlienBlood suggested, I couldn't find any leaks.

I tried the stomp test to see if the computer recognized any problems, it doesn't.

I took the intake off and checked to make sure I had hooked up everything correctly, I have, and I also replaced the fuel injector temp sensor

I have just put it back together and the same result, no difference

if I take the ICV and unplug it the idle starts to fluctuate irratically, so I believe it is working. The idle stays pretty constant, it just climbs higher and higher.

I don't have a means to rest the resistance of my O2 sensor at the time, you think that could be it?

DesktopDave · « **Reply #6 on:** September 28, 2012, 10:01:26 PM »

You definitely got a 1-4-4-4 on the check engine light, right? No light at all isn't what we're looking for. The early Motronic isn't very good at detecting faults, but it is good at giving hints.

When you removed the intake, how did you reseal the gaskets?

I still suspect one of the temp sensors. I'd normally suspect a cracked throttle cable or defunct ICV, but your idle climbs as the car warms up, right? That leads me to believe that the computer (DME) is mistakenly still running the cold-start enrichment routine. That's also called 'open-loop.'

So eliminate the sensors one by one. Do you have a copy of the BMW Electrical Troubleshooting Manual? If not, google 'wedophone bmw manual' and download it from them.

I know you replaced the coolant temp sensor. Test it anyway. I've had brand new sensors that failed. Also be sure to test the air temp sensor in the AFM (pins 4&5). Also run a quick check on the TB sensor - if your TB was mis-adjusted by a previous owner the car will never be able to compensate for a correct idle speed. There should be a paint mark on the throttle stop screw - BMW wanted to be sure their techs knew if someone had messed with that adjustment. Hopefully nobody messed with the AFM spring...that can also cause difficulties.

YYZE30 · « **Reply #7 on:** October 15, 2018, 10:28:47 AM »

Did you ever fix this problem... I know its an old post.

I just did the MUI and I have a high idle at 1K.. cold start its great at 850rpm... once it gets hot she's gets up to 1000-1100 rpm.

I didn't use vacuum hoses and used a heater hose... could this cause an issue?

DesktopDave · « **Reply #8 on:** October 15, 2018, 08:58:53 PM »

I'd check the usual culprits, air leak, temp sensor, etc.

And...are you sure you're not an idiot just like me?

I hate to admit this, but when I did my heater delete I didn't mark the plugs. They somehow ended up in the wrong places. IIRC the CLT harness was plugged into the oil pressure sender...so the DME didn't get the correct temp signal from the CLT sensor. The DME never shut off cold start enrichment, so once the motor warmed up it would idle high, running really rich. We had some fun tracking that one down!

YYZE30 · « **Reply #9 on:** October 16, 2018, 07:36:42 AM »

I did mix one of them up... it was the oil pressure unit and the gauge on thermostat. I had a check engine light come on and I reversed those two and cleared the codes. I have installed new oil pressure sending unit, and both temp sensors below the lower intake manifold.

I did try to clean the FPR with carb cleaner not sure if that messed up anything... also the AFM when I had the intake off to clean but used a rag as opposed to spray and was careful with the probe.

Would the check valve in the brake booster affect anything?

Other then that, two of my fuel injectors broke off on the bottom plastic, I did replace all the lower o-rings with new. Not sure if this is fuel related of hose.

DesktopDave · « **Reply #10 on:** October 16, 2018, 04:59:43 PM »

I wouldn't think the FPR would be bothered by carb cleaner. The AFM is a pretty robust thing too. If the check valve wasn't bad before you did the work, it's likely OK. Did you check to be sure the heater hose isn't collapsing? They can do that at high vacuum (idle), but it'd be easy to notice.

The lower fuel injector plastic is replaceable too, you can buy kits with those parts very cheaply. Here's a cheap OEM-style set for BMW sixes.

YYZE30 · « **Reply #11 on:** October 16, 2018, 06:32:57 PM »

How can I check the hoses?

I should probably install proper vacuum line hoses, start with easy stuff first because I don�t want to replace unnecessary parts.
I will install a new gasket between the afm and the air filter intake as well.

Thanks for the link, I didn�t realize that you can replace those. Phew!

DesktopDave · « **Reply #12 on:** October 20, 2018, 08:12:40 AM »

Start the engine, open the hood, check to see if the heater hose is collapsing under pressure?

The gold standard for vac leaks is the 'smoke test'. Google it. Some old timers will use a cigar; IMHO that smells too bad. It's not hard to build a testing rig with a bike pump, beekeeper's smoker, etc.. I'm not making that up, LOL. It's totally true!

YYZE30 · « **Reply #13 on:** October 20, 2018, 06:12:57 PM »

I�m familiar with the beekeeper smoker lol

Not sure what roll this plays but when I lift the clutch at the point where the car wants to lurch forward and if I hold it there along with the brake it idles perfectly at 850. Once I release the clutch it jumps back to the 1k area
and idles there. The hoses do seem soft and mushy after the car is heated up.

Just to confirm, the valve cover hose goes below the TB and the ICV hose goes to the bottom of the intake elbow?

Also, the spark plugs wires run from the front of the car going back... 1/2/3/4 ?

I ordered some performance vacuum hose from http://www.hiperformancestore.com/ I also ordered the fuel injector tops and will replace all four.

DesktopDave · « **Reply #14 on:** October 21, 2018, 09:12:13 AM »

Quote from: YYZE30 on October 20, 2018, 06:12:57 PM

Just to confirm, the valve cover hose goes below the TB and the ICV hose goes to the bottom of the intake elbow?

Also, the spark plugs wires run from the front of the car going back... 1/2/3/4 ?

Yep, VC hose to the TB, ICV into the intake elbow. The VC needs negative pressure, has to be downstream of the throttle plates. ICV needs to bypass the TB.

Yep, plug wires go 1/2/3/4 to cylinders 1/2/3/4, from the radiator to the firewall. You'd be surprised how many owners have tried to connect coils based on the firing order!

The only thing that comes to mind based on your throttle test results is the throttle body switch might be slightly out of adjustment. I'm not 100% sure what type of switch BMW installed on our cars, might be a variable-resistance version. That's a problem with owning lot of BMWs, it's hard to keep track sometimes! How's that for a first-world problem?

Author Topic: High idle, she won't come down. (Read 8822 times)

Sophia69IS

High idle, she won't come down.

ti_tony

Sensor

DesktopDave

High idle, she won't come down.

Sophia69IS

High idle, she won't come down.

colin86325

High idle, she won't come down.

Sophia69IS

High idle, she won't come down.

DesktopDave

High idle, she won't come down.

YYZE30

Re: High idle, she won't come down.

DesktopDave

Re: High idle, she won't come down.

YYZE30

Re: High idle, she won't come down.

DesktopDave

Re: High idle, she won't come down.

YYZE30

Re: High idle, she won't come down.

DesktopDave

Re: High idle, she won't come down.

YYZE30

Re: High idle, she won't come down.

DesktopDave

Re: High idle, she won't come down.