I'm trying to work through some idle issues. At this point I'm all self-taught using the Bentley and reading the Brickboard. Thanks for any help you can provide.

Here are the symptoms:
-On a cold start (I haven't checked a warm restart) the rpms rev to about 1500 and then settle back towards 750-800. I say settle towards because the trip from 1000 to 800 seems to take quite a while, 15 seconds or more. Afterwards the car idle is steady at about 800.
-This behavior continues as the car warms up. When I put the clutch in, the idle settles but slowly.
-Here is the confusing bit. When the car is warm and idling at a stoplight for about a minute, the idle speed will increase smoothly to about 1000 rpm and stay there.
-Wherever the idle is, it seems consistent. It does not dip and surge every few seconds or anything like that.
-The car starts, drives and runs well otherwise.

Here is what I've done:
-Checked for vacuum leaks. Everything looks good to me, but being a bit of novice I could be missing something.
-Check for codes in both 2 and 6. 1-1-1 from both.
-Cleaned the IAC valve. It did it when I was in doing the breather box and intake manifold gasket a few weeks ago.
-Tested the IAC. The lowest ohm reading I could get was 9.4 ohm, which is a little high according to the Bentley. (Too high?) I also applied battery voltage to it and it seems to move open and closed easily. (Protip: Use something to keep your test clips from falling together on the IAC. :)
-Swapped in a clean junkyard IAC which was actually worse than the original.

My questions:
-I read somewhere (the FAQ maybe) that dirt at the IAC connector could cause something like this. Anyone have experience with this? How do people clean their electrical connections?
-Should I be chasing something other than the IAC? If so what?
-I've got EGR. Does the EGR valve contribute exhaust to the intake at idle? Could a leaky EGR valve give these symptoms?
-I remember a post recently about a cheap aftermarket IAC, but I can't find it. Anyone remember? Maybe I'll need it.

Thanks,
Spencer

I've been meaning to write back for some time.

The last thing that I replaced was the climate control check valve and the associated 3/8 inch hose to the intake. It took care of the whoosh/hiss under acceleration and on shutdown (a symptom that I failed to report in my original post).

I'm pretty happy with the idle now. The weird rising idle is gone and it is consistent around 800 rpm.

The remaining oddity is that the rpms still decrease slowly between 1000 and 800 when I put the clutch in. I'll mull that one over and start a new thread if I can't figure it out.

Thanks Trevor and Phil!

Put in a new coolant temp sensor today. It was a good experience. It's tight under there with the manifold on.

The symptoms are unchanged. Still idles high when hot. Still idles well at 750ish before it is warm.

Pulling the IAC today I noticed that the contacts are darkened on both sides. So I'll reiterate a question from my first post: What's the best way to clean electrical connections at the IAC, TPS, etc?

"Still idles high when hot. Still idles well at 750ish before it is warm."

When the coolant is cold, presumably the ECU tries to keep the idle at a programmed point (750 rpms). But when the coolant is warm, the ECU may be feeding fuel based on the O2 sensor output. If too much air is entering then a matching amount of fuel will be added to maintain O2 sensor output.

So, could your throttle plate be open a bit at idle? Or you have a vacuum leak?
--
1980 245 Canadian B21A with SU carb, M46 trans, 3:31 dif, in Brampton, Ont.

I'm pretty sure the throttle plate is shut. I'll check again.

I'll test for vacuum leaks. I have a vacuum pump. I was thinking I might use it as a gauge while I plug different ports on the intake manifold. Is this a good approach?

"I was thinking I might use it as a gauge while I plug different ports on the intake manifold. Is this a good approach?"

Yes. Try pulling and plugging all the vacuum ports (eg. brake booster, passenger compartment air controls). If idle rpms drop then the problem lies there.
--
1980 245 Canadian B21A with SU carb, M46 trans, 3:31 dif, in Brampton, Ont.

I'm back. I replaced the booster hose and the problem persists. The car runs better, but still idles high when warm.

Looks like I may have had multiple vacuum leaks. I'm going to keep searching. If I can't find anything then I'll see if I can adjust the throttle plate, cable and TPS.

You and Swedish Baklava are running neck and neck to which gets theirs fixed first.

Check out his recent posts and responses on what he is about to do.

As far as cleaning connection a finger nail filing board can get down in there and clean the crud off.

I take Scissors and trim it to a real narrow tip and even thin it down until it scraps just with one side if needed.
I protect the terminal with a little LPS 1 or 2 for good measure.

Phil

Ha! I've seen some of Swedish Baklava's other posts. If he has the time and knowledge to do things like replace a center support bearing, then I'm sure to lose.

Thanks for the tip about the file and the LPS. And also for the reference to another relevant post.
-Spencer

Looks like it was the brake booster hose. Both it and the check valve are original. The car idled steady at 750 (and much quieter than before) for 10 minutes with that port on the intake plugged.

Wiggling the check valve produced a hiss, so I'm assuming the check valve is probably ok. I might replace it anyway. I'll call my local parts place tomorrow and see what they can do for me.

I'll report back with the final result when I'm done. I also realized that I reused the egr gasket on the intake after the breather box replacement, so I may replace that too.

Thanks for your help. I learn a lot every time.
-Spencer

Ok I'm back with a report.

I pulled the connector off the LH computer and ran through testing resistances as described in the Bentley.

The TPS tested good. My previous testing must have been probing on the wrong side of the TPS circuit(s).

For the Coolant temp sensor I have two data points. I didn't see how to get a third where I actually knew the tempurature.

After sitting over night, about 60 degrees ambient tempurature, I got 3500 ohms. (I just moved from Pittsburgh to Southern California. This no winter thing is weird!) At operating tempurature after errands around town, 260 ohms.

The second reading was taken soon after I turned the car off. When I turned it off it had just executed its surge in idle from 800 to over 1000.

This seems just ever so slightly out of spec. The car has 238,000 miles and the coolant temp sensor hasn't been replaced in the 6-7 years that I've owned it. I think I'll just replace it, because the part is pretty cheap.

Other notes from the testing:

-Ran into another error in the Bentley which has been documented on the board, but is not in the post I linked previously. On 241-15, the test results for the O2 sensor are reversed. Link.

-Most of the grounds that I tested from the LH computer have a resistance of 1 ohm. So I'll go get some fine grit sand paper, clean them up and see if that helps.

Thank you everyone for your input. I'll keep you posted.
Spencer

I had a random high idle in my 86 240 with the LH2.2. It turned out to be the ECU temp sensor, it was randomly going high resistance making the car think it was at the North Pole.

This is the most likely cause, but before you push the money button, test the resistance of the ECT at the ECU connector. Most likely cause would be a higher than normal resistance in the circuit due to a poor electrical connection. Only take this path if you're sure the CTS is working properly.

Test the ECT while connected to the harness at 3 different temps, freezing, boiling water and room temp. Compare the values to the greenbook or Bently's chart. A consistent offset in the +X direction means a bad high resistance connection. A non-linear response, especially for the ice point usually menas a bad ECT.

Hi Pete,

I didn't see how to get three data points with the coolant temp sensor still in the car. (See my post below.) It seems easier to pull the old one out and stuff a new one in than it does to pull the old one for testing.

For the hell of it, I will test the new one as you suggest before I put it in the car.

Thanks,
Spencer

Thanks for the input. This sounds plausible too. I probably should have replaced it when I had the intake off to do my breather box.

I'll search the archive to see if you can do it with the intake on.

I guess it's important to mention here that my '91 california car has LH 2.4. So I've got the TP switch rather than the TP sensor.

So in trying to test the TPS I ran into a known error in the bentley. Here is a post from lucid: Bentley Errata

Here is the relevant testing information: TPS info (thanks again to lucid)

So I ended up peeling back the rubber on the TPS connector with it plugged in and probing wires from there. The second linked post of lucid's says that the yellow and white wire is the one that signals throttle closed.

Probing the yellow and white wire gives continuity to ground regardless of the position of the throttle plate. I get a similar result from the white and blue wire to ground.

A few questions:
Is this consistent with the symptoms I've described?
Is this a typical TPS failure?

-Spencer

http://www.volvowiringdiagrams.com/volvo/240%20Wiring%20Diagrams/Volvo%20240%201990.pdf
Fig. 2: Computer Engine Control (Grid 4-7) shows the TPS.

Continuity should change with throttle plate opening and closing.

--
1980 245 Canadian B21A with SU carb, M46 trans, 3:31 dif, in Brampton, Ont.

Thanks for the wiring diagram. That's much clearer than what's in the Bentley.

I'll retest the TPS this week to confirm before I order a new one.

Hello-
read your post with curiosity as I too have similar issues with a '89 740 GLE. I suspect it may be the TPS in my case as I have gone through every other item in this process.
there is a current post and you may have read it. Posted by "dnarby" January 20 re: '92 740GL Regina.The responses have been pretty useful, and it pertains to the problem I'm having. Check it out.

Volvosenior
--
89-740 GLE;91-940 Sedan ;98-V90 Wagon ___ all running well

Thanks for the reference! I'll take a look at the TPS tomorrow and report back.