slightly high/low idle once warm

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lannvouivre
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Re: slightly high/low idle once warm

Post by lannvouivre » Sat May 28, 2016 9:33 pm

Does it have OBD1? If it does, and if OBD1 has engine data, you can check O2 sensor fuel trims to inspect for a leak.
But...did you try hitting it with a hammer?

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dlb
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Re: slightly high/low idle once warm

Post by dlb » Sat May 28, 2016 11:07 pm

lannvouivre wrote:Does it have OBD1? If it does, and if OBD1 has engine data, you can check O2 sensor fuel trims to inspect for a leak.
it is obd1 but i don't know what you mean about engine data or checking o2 sensor fuel trims. what are those things and how do you check them? although i should say i've been very thorough in my search for a vacuum leak. i've disconnected and plugged every vacuum port and vacuum-operated device, and sprayed both propane and carb cleaner all around with no rise in rpm's.

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lannvouivre
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Re: slightly high/low idle once warm

Post by lannvouivre » Tue May 31, 2016 6:36 am

You would need to plug in an OBD1 scanner. OBD2 systems have many parameters that can be pulled up and examined by a scanner. I have never scanned an OBD1 car, let alone an OBD1 Japanese car, so I don't know if you can pull anything from them except codes. Google has not been helpful for this.

OBD2 vehicles can show you sensor readings and such. The front O2 sensor readings will tell you how much fuel the computer is adding to maintain the correct stochiometric ratio of fuel to air. If you have a vacuum leak, the O2 sensor will see an excessively lean mixture and try to compensate with additional fuel.

I think your problem is still likely to be a leak somewhere in your intake system. Check your fuel injectors where they mate with the intake or head, as vacuum leaks can develop there. It could also be a pinhole or crack in the intake manifold. If you were running rich, you'd likely have a horrible idle and the exhaust would also smell pretty bad.

https://www.youtube.com/watch?v=zMok2y05jNE

Here is another way to look for the leaks. If the smoke is coming out from an area you can't see, though, it's harder.

When you were testing the EGR, did you block it off? How did you narrow it out?
But...did you try hitting it with a hammer?

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Re: slightly high/low idle once warm

Post by Petros » Tue May 31, 2016 11:40 am

David,

to add to what lannvouivre wrote, just to clairfy. Both OBD1 and 2 system actually has the ability to show all of the engine parameters that the system uses to adjust the fuel mixture. with a full scanner, not just a code reader, you can see in real time intake air temp, coolant temp, rpm, fuel flow, airflow, mixture, etc. Often with this information you can find problems that do not throw an error code. When something is within normal range, but still wrong for the actual conditions.

Our Ford one ton for example, and all fords in general, are notorious for having bad throttle position sensors. But it does not code, because the error is still within normal parameters, but off for the actual conditions. The computer thinks you are full throttle, even at idle and part throttle condition, because the TPS defaults to full throttle when it wears out. The result is it runs way too rich, and the TPS also sends a signal to the auto trans and delays shifting to a higher rpm, so it makes high rpm jerky shifts (making you think the transmission is failing), and it gets bad fuel economy. I did not know this about Fords at the time, but it was not until a client of mine who had a (costly) portable full system diagnostic scanner hooked it up for me as a favor. He scrolled down all of the out put, idle was a 700 rpms, but the TPS showed full throttle. the part was only $35 to fix it, but any shop would have charged me $100 just to test it.

So when you get no error code, without the full data out put, you have to try and guess what sensor(s) may be giving bad signals. So you either have to trial and error swapping out known good sensors, or see if you can use a volt-olm meter to individually test all of the sensors are, not just within normal range, but also putting out the correct reading for the conditions.
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dlb
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Re: slightly high/low idle once warm

Post by dlb » Wed Jun 01, 2016 9:50 pm

i tested something today to rule out vacuum leaks. i let the engine warm up and start to idle high and then inserted a wire between the terminals used to check engine codes, set timing, set idle, etc. when i did that, it idled normally. i could step on the throttle and the revs would come back down to the normal level, no problem. so i know that it is definitely part of the ECU system causing the problem.

i have tried unplugging all the various sensors one at a time, looking for any change in the symptoms, but found nothing. that was a while back so i'll have to take another look at the various sensors and make sure i didn't miss one. i just got my FSM back from a friend so i hope to do this in the next few days.

thanks for all the continued suggestions.

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Re: slightly high/low idle once warm

Post by dlb » Fri Jun 03, 2016 2:46 pm

i forgot to mention that i have a similar thread going over at the ae95 forum. one of the guys there is a pro mechanic who has access to the TIS (toyota information system) which is basically an online version of the FSMs. he said that my FP results are in line with what is in the TIS, and mentioned that since the info differs between the TIS and the FSM, the TIS is probably correct. he said it is corrected and updated whenever they find errors, whereas the FSM is printed with errors and you won't know where they are unless you find them or get the updates and corrections from toyota. long story short, my FP is fine.

i decided to start testing sensors as per FSM recommendations, as opposed to just unplugging stuff and watching for a change in symptoms, and my o2 sensor failed the test so i ordered a new one. it's only $50 but if i put it in, test it, and get the same results, i'm going to be very annoyed.

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lannvouivre
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Re: slightly high/low idle once warm

Post by lannvouivre » Sun Jun 05, 2016 10:25 am

If the O2 sensor doesn't fix it, then you're probably either looking at the ECM itself having a fault, wiring damage, or the O2 sensor is from the wrong brand or something.
But...did you try hitting it with a hammer?

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Re: slightly high/low idle once warm

Post by dlb » Sun Jun 05, 2016 10:41 am

already tried swapping out the ECM with a known good one.

i got the sensor and hope to replace it today during a lull at work.

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