1700 RPM idle speed, can't find solution.

[igreenrover]

Dear All

Can anyone help with this?

I have an intermittent problem with the idle speed on my 89 SE. About 1/2 the time it runs at the correct idle speed, and the rest of the time it runs about 1700rpm. Using Freescan I can see that the ECU has a correct target idle speed but is unable to achieve it. I've cleaned the idle air valve and it 'appears to be working ok' in as much as it moved in and out when starting the engine with the valve out. I can't see any obvious problems but have a short scan of the car running at about 1000, and another at about 1700:

http://idisk.mac.com/garethspencer/Public/1st.csv

http://idisk.mac.com/garethspencer/Public/2nd.csv

The second scan was made after re-setting the idle air controller (through Freescan) but if I rev the engine a little it will run at 1700rpm again. Again, if I stop and then re-start the engine it will run about 1000 and then suddenly move up to 1700 after about 10-20 seconds.

Darn difficult to drive in traffic like this, and reverse is a nightmare when its hot and running at this speed. I've re-set the ECM and it was new last year but I had this problem before changing it.

Thanks in advance
Gareth

[PatHeald]

I experienced similar symptoms on my carbed '87 HC Turbo.

Just a suggestion, but do the SEs have a throttle jack? The one on my car is operated by a solenoid and was the source of great irritation to me, until I disconnected it.

Try here:

www.pistonheads.com/gassing/topic.asp?t=69116&f=17&h=0&hw

or here:

www.pistonheads.com/gassing/topic.asp?t=52007&f=17&h=0&hw

Cheers

Pat

[igreenrover]

Pat

Thanks for the reply.
The SE has a throttle jacking capsule that is used in conjunction with the exhaust valve for rapid exhaust warm-up. I've pulled the vac line from it and no change, also checked that the armature is returned. Might be worth disconnecting it altogether though if no other suggestions emerge.

Gareth

[igreenrover]

I was wondering about the o2 reading? It seams quite erratic, especially as the engine is idling?

[Skerd]

I have had two different causes for a high idle. One way the IAC valve you already mentioned. The other was the fuel pressure regulator. It has been fine since this was replaced.

[igreenrover]

Is the regulator at the rear of the fuel rail to the right of the charge cooler? With a Vacuum line attached?

Can anyone tell me how to check it? (Pressure, measurement point etc..)

[Dr.Hess]

Check the regulator by hooking a fuel pressure guage (available at your local auto parts store) to the fuel rail at the port. I don't know what the Esprit fuel pressure should be, but it is typically around 42 PSI on most EFI systems. I am sure Jim or Tim will chime in with the correct reading.

You have gone around checking for vacuum leaks, right? Spray a little WD-40 or carb cleaner around all the joints and connections while the motor is running and listen for change in RPM?

Dr.Hess

[MikeyRide]

Isn't that IAC value way out of spec? It may be pegged wide open.

I just adjusted mine but I can't recall what the correct value was. 10-25?

Interesting that the ignition timing is so different between runs too. Could both be trying to compensate for fluctuating fuel pressure?

[arium]

Personally, I'd look at your tps. I don't know if you're throwing a code for it or not but it seems stuck at .55. Interesting that your coolant sensor isn't roaming around either as they are sharing the same ground. I'd want to make sure J2B6 has continuity. The ecm will substitute a value to allow you to get home if it detects a tps fault.

Good Luck,

Steve

[igreenrover]

Thanks for the responses chaps.

Steve, the car was just idling so the throttle was never actually moved on the two logs. Later, I did move the pedal through the range to see if the % reading corresponded with movement and it appeared to be about right. Erm, I think you are looking at the engine start temp?

Mikey, about the IAC valve. I notice that in the second log when the RPM is about correct the IAC position changes quite a lot through time but in the first log its actually fixed at 85 through the whole run. Do you know if this is the actual position of the valve or is it where the ECM thinks it should be? Could be a problem?

Gareth

[MikeyRide]

igreenrover said:

Mikey, about the IAC valve. I notice that in the second log when the RPM is about correct the IAC position changes quite a lot through time but in the first log its actually fixed at 85 through the whole run. Do you know if this is the actual position of the valve or is it where the ECM thinks it should be? Could be a problem?

I'll have to check the engine management manual. My (uneducated) guess is that it may be compensating for something else such as fuel pressure. It's easy enough to adjust though - you just need to turn in the throttle stop screw, cracking the throttle plates a tiny bit. IIRC, 1/8 of a turn dropped my IAC reading some 20 pts (I don't think they're units of any kind) but really didn't seem to affect the engine at all.

[MikeyRide]

Some bits about IAC operation:
max value is 170 (wide open, passing the most air)
min value is 0 (completely closed)
Ignition ON, engine OFF, it should display ~170 counts.

It doesn't make any sense that you're stuck at 85 with the car running 1700rpm. The ECM should command it to lower values. "The Tech 1 will read the ECM commands to the IAC valve in counts." So Freescan is reporting what the ECM is requesting. I would expect to see zero in the case of stuck at high idle.

BTW, I didn't see you mention any codes. You have a code 35, right?

"The ECM reseets the IAC valve by seating it (fully extended) to establish the zero count position then drawing it back to the desired position. This will occur only once during each ignition cycle, when vehicle speed increased above 20 mph on moderate acceleration. The IAC valve will not be reset again until the ignition has been turned "OFF", the engine restarted and teh car then driven above 20mph. When servicing the IAC valve, it should only be disconnected or connected after the ignition has been off for at least 10 seconds. This allows time for the ECM to move the IAC valve to the 170 count position where it is "parked" while the ignition is "OFF". If this procedure is not followed, the ECM will lose track of the IAC valve position resulting in starting or idle control problems."

Phew!

[igreenrover]

Thanks for that!

I'm not getting any fault codes at all. I'm going to try a new valve today as I already have one to try but from what you describe its not going to be the valve that's at fault. Presumably the ECM is holding the valve at that position because of some other variable?

So, that only leaves the Fuel Pressure, and the O2 reading as the last remaining possibilities from the original suspicions. Any other Ideas. I'll go over all the vacuum lines again.

[MikeyRide]

I was thinking about this some more. If the IAC isn't getting adjusted and you're not getting fault codes, maybe the ECM doesn't think you're at idle. Code 35 is supposed to be set if the car can't keep idle within 200rpm of desired.

EDIT: wrote "TPS" when I meant "IAC"

>> Edited by MikeyRide on Friday 10th September 14:51

[igreenrover]

Hmm

I 'occasionaly' get a VSS error, normaly when the RPM is running closer to 2000 RPM. Dose this open any other doors?

I've never had any other codes since new ECM last summer.

[MikeyRide]

igreenrover said:

I 'occasionaly' get a VSS error, normaly when the RPM is running closer to 2000 RPM. Dose this open any other doors?

You get the VSS error when you're driving? Or when it's doing its high-idle thing?

I'll check the manual.

[igreenrover]

Never had it when driving, had it just a couple of times when its been idling particularly fast. Before even driving the car away. I.e start the engine, it runs about 1900 and after about 30 seconds I've had this fault.

When I finish work today I'm going to pull all the valc lines and electrical plugs and inspect everything. If I remove the TPS is there a procedure I need to use to set it back up?

I’m lost with this now.

[MikeyRide]

igreenrover said:

If I remove the TPS is there a procedure I need to use to set it back up?

Yes, I think so. I wouldn't remove the TPS w/o the setup procedure in front of me. Your TPS voltage looks good anyway. The manual states 660-700mV spec BUT also says anything over 400mV is OK. My car is 510mV at idle.

Since you're getting a VSS error, it makes sense to look in that direction. Does anyone know if disconnecting the VSS will be read as zero mph or will it set a fault?

[igreenrover]

Ok, turns out I can't get a new IAC valve through normal part suppliers, can get the actuator no problem but nothing to match the valve seat. Price from SJ is not so bad for this though so if needed then thats they way I will go.

So, I removed the C/Cooler and all the old vac lines around there and replaced them. did notice the small rubber elbow that connects to the hard plastic line didn't look so good and so changed that. Also under the cooler there is a tee section that screws into the inlet manifold that didn't appear to be so tight.

Currently its running fine, about 950 on the RPM gauge. Only driven about 6 miles but a bit of start stop in there with no ill affects. If its OK in the morning I'm going to drive from Manchester to London, then to Bournmouth and then back next week so let hope its fine!

Cheers,
Gareth

[Dr.Hess]

Are you suggesting...

Vacuum leak ....??