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Old 04-30-2021, 10:37 PM   #1
ITA
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Default 1988 Volvo 240 - Surging Idle

I just changed the coolant temp sensor (fuel injection sensor) and the coolant temp sender sensor. I had a constant idle of 1500 rpm regardless of whether the engine was cold or warm and my temp gauge was not working.

I removed the intake manifold and cleaned the TB and replaced gaskets. After I put it all together, it surges terribly at idle, going to to 1500-2000 rpm and dropping until it almost dies and up again. Each interval lasts about 2-3 seconds. I do not understand what is happening. I checked all the hoses, sensors, and grounds I undid, and I didn't miss any. I did mess up the ignition coil wire (the wire came out of the boot on the distributor end; I can stick it back in, but I don't think it should be that way). What should I be looking at? Bad IAC all of a sudden? Bad TPS (it seems adjusted correctly)?
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Old 05-01-2021, 01:28 AM   #2
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Originally Posted by ITA View Post
I just changed the coolant temp sensor (fuel injection sensor) and the coolant temp sender sensor. I had a constant idle of 1500 rpm regardless of whether the engine was cold or warm and my temp gauge was not working.

I removed the intake manifold and cleaned the TB and replaced gaskets. After I put it all together, it surges terribly at idle, going to to 1500-2000 rpm and dropping until it almost dies and up again. Each interval lasts about 2-3 seconds. I do not understand what is happening. I checked all the hoses, sensors, and grounds I undid, and I didn't miss any. I did mess up the ignition coil wire (the wire came out of the boot on the distributor end; I can stick it back in, but I don't think it should be that way). What should I be looking at? Bad IAC all of a sudden? Bad TPS (it seems adjusted correctly)?

You can crimp the IAC hose to slow airflow(although it's possible your issue could be unrelated to the IAC).
LH 2.2 I assume, what else can you tell us about the motor/is the timing advanced ?
Checked infamous intake accordion hose for vacuum leaks ?
Is there anything about the injectors you can tell us/leaky injector/s ?

* if all else fails contact cleanflametrap

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Last edited by Otto Mattik; 05-02-2021 at 03:57 AM..
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Old 05-01-2021, 06:40 AM   #3
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...Bad TPS (it seems adjusted correctly)?
This is where I would look. If I were to remove the plug from the TPS, this is exactly how the idle would act. The TPS can ingest a lot of blowby oil eventually getting into the snap action switch, but more likely it isn't clicking solidly when you take your foot off of the throttle, or the wire terminals at the electrical connector have backed out if you disconnected it during the TB cleaning. Don't set the "click" too precisely at the throttle stop, like the advice usually says -- make sure the throttle travels a small, but clearly repeatable amount off of the stop before it clicks.
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Old 05-02-2021, 12:41 PM   #4
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Thanks everyone for the tips. I unplugged the tps and it was still doing the exact same thing. I scrounged around my garage and found a couple spare tps's. I am going to swap one in and see if the issue continues. I will update once redo or if further troubleshooting is necessary.
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Old 05-03-2021, 08:02 AM   #5
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Originally Posted by ITA View Post
Thanks everyone for the tips. I unplugged the tps and it was still doing the exact same thing. I scrounged around my garage and found a couple spare tps's. I am going to swap one in and see if the issue continues. I will update once redo or if further troubleshooting is necessary.
Here is a youtube video showing diagnosing what should be the same IAC as your car. I had an LH 2.2 IAC that showed within specs yet still caused a higher than normal idle (1200-1500rpm). I didn't watch the entire video, but thought it interesting he mentioned getting the diagnosis instructions from Autozone (go ahead and finish your TPS diagnosis first as you started there).

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Old 05-04-2021, 04:08 PM   #6
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So, I changed the TPS with a spare. The one that came off my car had quite a bit of oil or possibly throttle bottle cleaner. It started pretty good with the spare for about 5 seconds, then it went back to surging idle.

I unplugged the IAC to see if anything would change and something did happen, it wouldn't idle at all. I also thought I should check the AFM. After plugging the IAC in, I unplugged the MAF and it was idling solid at 1500 RPM. I didn't let it run long enough to see if the RPM's would go down as the engine warmed up, but could I have a bad MAF?
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Old 05-05-2021, 02:45 AM   #7
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Quote:
Originally Posted by ITA View Post
I just changed the coolant temp sensor (fuel injection sensor) and the coolant temp sender sensor. I had a constant idle of 1500 rpm regardless of whether the engine was cold or warm and my temp gauge was not working.

I removed the intake manifold and cleaned the TB and replaced gaskets. After I put it all together, it surges terribly at idle, going to to 1500-2000 rpm and dropping until it almost dies and up again. Each interval lasts about 2-3 seconds. I do not understand what is happening. I checked all the hoses, sensors, and grounds I undid, and I didn't miss any. I did mess up the ignition coil wire (the wire came out of the boot on the distributor end; I can stick it back in, but I don't think it should be that way). What should I be looking at? Bad IAC all of a sudden? Bad TPS (it seems adjusted correctly)?
In your initial post you mention a constant idle of 1500, and the surging began after replacing the CTS ?

My only experience with a bad LH 2.2 IAC was one that idled too high, and it was worse when the engine was hot. Like I mentioned on mine, it was within spec, cleaning made no difference and the problem only went away after replacing the unit. It's also very possible the issue has nothing to do with your IAC, mine never surged, it only idled high.

The video shows how do a resistance test on the IAC(it's a good place to start).

I assume you have not changed the timing ?

Also not sure if you're aware of this detail, but do not disconnect computer related components with the ignition on. Turn engine off, turn key off prior to disconnecting/connecting electronic components.

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