New twist on old issue - warm-up idle

I have an 87 EXI. I have read quite a bit of information of the "bouncing" idle issue and the fixes. There are even some You Tube videos on this issue. What I have is slightly different and is not a big issue for me but is annoying. The engine starts up good and idles at about 2000 RPM. As the engine warms up the RPM's decrease (after about 2 minutes). At around 1400, the engine will bounce between 1400 and 900 for about 45 seconds. After the bounce the engine returns to about 1200 RPM and continues to warm up properly with no more bouncing. It sorts itself out without any throttle movement from me. It drives normally after this with normal idle. Because the erratic idle only happens at a specific point in the warm-up process I think it has something to do with the coolant temperature. When the coolant temperature is hot it is fine; when it is cold it is fine. What sensor sends the signal of the water temperature that controls the idle speed? Where is it located and what is is called? Am I even on the right track with thinking it is related to the water temperature? As I only have to live with this situation for about 45 seconds during the warm-up, I could learn to live with it but it would be nice to change as Spring has come to Canada and it is warm enough to work on the car again. Thanks for any help.

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Originally Posted by omianan

I have an 87 EXI. I have read quite a bit of information of the "bouncing" idle issue and the fixes. There are even some You Tube videos on this issue. What I have is slightly different and is not a big issue for me but is annoying. The engine starts up good and idles at about 2000 RPM. As the engine warms up the RPM's decrease (after about 2 minutes). At around 1400, the engine will bounce between 1400 and 900 for about 45 seconds. After the bounce the engine returns to about 1200 RPM and continues to warm up properly with no more bouncing. It sorts itself out without any throttle movement from me. It drives normally after this with normal idle. Because the erratic idle only happens at a specific point in the warm-up process I think it has something to do with the coolant temperature. When the coolant temperature is hot it is fine; when it is cold it is fine. What sensor sends the signal of the water temperature that controls the idle speed? Where is it located and what is is called? Am I even on the right track with thinking it is related to the water temperature? As I only have to live with this situation for about 45 seconds during the warm-up, I could learn to live with it but it would be nice to change as Spring has come to Canada and it is warm enough to work on the car again. Thanks for any help.

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you check your idle air control valve?

^ That. Make sure the line aren't clogged or you could be low on coolant.

If the cooling system hasn't been flushed i suggest doing so with a new thermostat. Also clean the IACV and try again if it continues doing it then you have a bad IACV, Low coolant or clogged lines.

I have this same issue. I put in some wonder coolant, lifetime fill type stuff and I've had a brief bouncing idle issue ever since. If you aren't using a $35/gal lifetime coolant, then I would guess that you're low on coolant. If you are, then you'll need to fill and bleed the system properly or it will continue.

Thanks for all these responses. Since my original post I have viewed a couple of YouTube videos on cleaning the Idle Air Control Valve. I tackled that job this morning. Had to take the top part of the air box off in order to get at the back two 10mm bolts that are closest to the air box. I took the two coolant lines off first before loosening the bolts. Everything came apart pretty easy. I sprayed throttle body cleaner into the two openings and let if fill up with cleaner and let it sit for a bit. I noticed little bubbles coming up in the cleaner like there was some kind of action going on. I also noticed that the two rubber sealant rings were flat instead of round which made them flush with the housing, not much sealing ability left in them. I got them out and they were hard. I found a couple of O rings that were a pretty close fit. Since they will not stay in place during the re-install procedure, I had to use a couple of dabs of white grease to set the O rings into. That way the O rings will stay in place while they are in the vertical position during the reinstall. When putting it back on with the bolts finger tight, there was a slight gap as the O rings were now proud of the housing but they compressed when the bolts were tightened, giving a good seal now. I also had a door courtesy light that was out so needed to be traced that problem down; found the connector behind the door panel was not plugged into the receptacle; now it is working. Just cleaned up the tools and came in for lunch.

I did use the bleeder screw by the thermostat but did not have any air in the system and it didn't make any difference hence the removal of the AICV today.

I also read about turning down the large flange inside the AICV to stop the bouncing idle but I didn't want to screw around with lowering the high idle at startup as that is what happens when that is done, apparently.

I am not using that pricey coolant so if this doesn't work, I am going to have to try that next.

That seems to have fixed everything. It warms up perfectly. Starts at 2000 RPM and drops at the appropriate intervals. It ends up idling at 1100 RPM when fully warmed up. No bouncing idle at any time during the warm up. Cleaning out the valve was what is needed to stop this bouncing idle. I would definitely recommend changing the two O rings if they have become hard as they can't seal very will if they are level with the housing and not extending past it. Took it for a 30 minute drive and it runs very nice now.

What is the recommended idle ? 1100 rpm's ?

The manual states 700 RPM plus or minus 50. I like a faster idle for a five speed standard so I increased it up a bit for the 87 EXi. My 89 LX (Carb) has an auto transmission and it is set to a lower idle speed but not as low as 700. At 700 RPM, I wonder how well the cam bearings get lubrication on an older engine.

No bearings it rides right in the metal in an oil bath. Low spring tensions since its over head cam so low pressure on the "bearing" surfaces. Fairly high oil pressure at idle and 50-65 psi at 3000 rpms.

Sounds like a good fix with the idle. You can turn down the cold idle with the fast idle valve plunger if your worried about cold ,dry starts. I prefer 1500 or less myself.


wp

Curios thing about this bouncing idle. If I wait till mid day (warmer air temperature) to start it up, it idles fine. If I start it at 6:00 am when the air is colder, I get the bouncing idle for a short period during the warm up. Even cleaning out the idle air control valve has not solved it completely, better than before, but not completely.

I'm going to say you have a coolant bubble in the IACV. Regular bleeding doesn't always get them. I have taken to jacking up the front of my car when I bleed coolant just to encourage the bubbles out.