New High Idle when Warm Problem (2 Viewers)

[Flank]

My 95 has been running strong at 262K. All has been as expected until yesterday and today when I started experiencing a high idle problem after driving the truck at normal operating temps:

I drove about a hundred miles to do a delivery, and when I pulled off the highway and then to a stop sign, the truck felt like it had weak breaks. As I stopped I realized that truck was idling high at stop and the weak breaking was actually the engine and tranny still trying to pull me along. When stopped, my idle was sitting at about 1400 to 1600 RPMs. This is strange. The only other time this had happened was last year when I had a stuck throttle cable, which was replaced. I pulled up the pedal and confirmed it was not sticking.

I then shifted to neutral and a very weird thing happened - the truck revved itself three times (as if I was rapidly pressing the accelerator pedal, from 1200 to 1800 RPMs. After the three revs, it settle down to about 1100 rpms. Driving the truck to the customer site was normal, outside of the high idle.

The three times I have driven the truck since, has been like this: normal start as expected, then after it warms up, it idles high at about 1000-1100 RPMs in Drive. Once, I shifted to neutral and it did the triple reving thing again. Other times it has not.
I run a Scanguage, and the engine temps have not gotten hotter then 190 during any of these occurrences. I popped the hood and confirmed that the throttle cables and rotation of the throttle body were normal and not binding up.

Any Ideas? The only idea i have found through search was to clean the throttle body may have the air intake valve plugged.

 

[Timpanogos Slim]

Weird.

idle air control solenoid?

Check for vac leaks?

 

[CJF]

I'd suspect the throttle position sensor first.

Also, pulling up on the gas pedal is not as definitive a test for a sticking issue as popping the hood and manually checking/closing the throttle.

 

[Flank]

I did pop the hood and work the throttle, confirmed that much.

 

[Muddy1]

Did you figure this one out? It sounds exactly like my symptoms. In fact, when driving along, sometimes it feels like the engine is just revving.

Thanks,

Muddy1

 

[stlcruiser]

Have you been using the cruise control? Same thing happened to me years back when exiting the highway after using the cruise control. Hasn't happened since.

Steve
94' 280,000

 

[Flank]

I think I have an ailing air idle control valve. I did remove, disassemble and clean, then reinstall. It is not as bad as it was, but still runs high in the 11-1200 range occasionally, but I cannot pin down a pattern of driving that causes it. The explanation of the AIC valve sounds perfect, as also occasionally, I get a slightly lower idle around 585 or so. So it seems to me that I may have a valve (this is motor driven) that is weak. To answer the Cruise question - has nothing to do with it in my case.

 

[CJF]

Are you going to replace the IAC?

Curious to see if that's it.

 

[94SRUNNER]

I think I have an ailing air idle control valve. I did remove, disassemble and clean, then reinstall. It is not as bad as it was, but still runs high in the 11-1200 range occasionally, but I cannot pin down a pattern of driving that causes it. The explanation of the AIC valve sounds perfect, as also occasionally, I get a slightly lower idle around 585 or so. So it seems to me that I may have a valve (this is motor driven) that is weak. To answer the Cruise question - has nothing to do with it in my case.

Flank,

Did you ever figure this one out?

I believe I have the exact issue, at least my symptoms are the same. And the idle air control valve is the first thing that came to mind, as the throttle cable is relatively new.

 

[Flank]

I did not figure this out. I bought a used throttle body with a AIC sensor cheap and swapped out the sensor. It seemed to (help) a little bit, but I still suffer from intermittant high idle and occasionally very low idle (400-600 rpms). I am still working on it...

 

[94SRUNNER]

I did not figure this out. I bought a used throttle body with a AIC sensor cheap and swapped out the sensor. It seemed to (help) a little bit, but I still suffer from intermittant high idle and occasionally very low idle (400-600 rpms). I am still working on it...

When you installed the new(used) IAC valve did you clean the carbon deposits off of it? If so how did you go about it. I too have a new(used) one and am going to swap it in.

 

[Flank]

Yes, I did. It was not as dirty as my original, but I cleaned it with Simple Green, disassembled and greased it.

 

[DARKNESS]

Could the kickdown cable be sticking and causing the throttle to be slightly open?

 

[94SRUNNER]

Yes, I did. It was not as dirty as my original, but I cleaned it with Simple Green, disassembled and greased it.

Good to know. Thanks for the information

 

[LuckyOreo]

I had similar symptoms where once the engine warmed up it would sometimes idle very high. the idle would go back down if I pulled on the pedal. I replaced the throttle cable and haven't had the issue since.

 

[Tools R Us]

I'd suspect the throttle position sensor first. ...

Agree.

... I run a Scanguage, ...

What does the throttle percentage read, is it the same when the idle is high? With the key to run, engine off, slowly open the throttle, does the reading change smoothy or have dropouts? Run the FSM volt meter tests on it for the idle switch.

 

[94SRUNNER]

So I went ahead and swapped in my new/used IAC valve last night. The old one looked a well worn and there was a very think layer of carbon deposit on it. I cleaned passage out as best as I could without removing the throttle body, but plan to pull the whole throttle body this weekend for a thorough cleaning.

This morning, once the truck had warmed up it behaved (idled) more normally than with the old IAC valve, but the true test will be on the drive home today when it is good and warm out.

Additionally I went through the TPS test that Kevin mentioned above and it checked out good.

 

[94SRUNNER]

A follow up from earlier today. On my way home I experienced the same high idle conditions as previously described, although it didn't seem as high before I swapped the IAC valve. Early this evening I tore into the throttle body to give it a once over. I thoroughly cleaned it (and it was very dirty) and while I was in there I change the spark plugs and cleaned up the MAF sensor.

Once everything was back together I took it for a test drive and while the ambient temps weren't as high as when I drove home, it was still rather warm. I got the truck up to operating temps and the idle was fairly normal. We'll see what tomorrow brings when I am able to get some day time temp driving in.

When I got back to my garage I was going over the FSM, I came upon page EG-155, which covers a component called the Throttle opener. According to the FSM it appears this component operates in a RPM range of 700-1000 RPM's. If the throttle opener has begun to fail, I wonder if this may be the cause of the elevated RPM's?

Thoughts?

 

[Joegasamanian]

This is my idle. I think it's normal?
I'm more worried about my oil gauge though at idle.

 

[DARKNESS]

650 is normal, so that's fine. Oil pressure gauge is low. On mine thats an indication I need to top it off. Could be a bad oil pressure sensor as well.