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Old 03-17-2017, 09:23 AM   #1
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Fluctuating high rpm after warm up

So recently the RPM at idle has changed. The RPM at cold start is great. Sits right at 1k-1100 rpm. After engine warms up though it will sit somewhere between 1500rpm and 2000rpm.

Things already replaced:
Throttle position sensor
idle air control valve (already adjusted all the way down)
replaced all vacuum lines

I will note that this didnt start until shortly after all vacuum lines were replaced.
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Old 03-17-2017, 10:14 AM   #2
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What year/engine/trans? I'd recommend putting this info in your signature.

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1990 Yamaha TW200.

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Old 03-17-2017, 10:22 AM   #3
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thanks. Just added in.

1989 2.5l ax-5.

more info on everything done so far can be found in my build thread.

1989 YJ 2.5L - Not running - sitting 8 years....
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Old 03-17-2017, 10:42 AM   #4
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Did you clean the IAC, or just adjust it? You replaced vacuum lines and then had the problem. Did you route them the exact same way? Do you have any vacuum leaks now? Did you put a vacuum gauge on it after the vacuum line replacements? Did you check for codes, even if you have no CEL? Did a vacuum line pop off? Tossing out ideas in no particular order.

Its been a while, does your TPS need to be adjusted? If so that can cause problems too.
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Old 03-17-2017, 11:16 AM   #5
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Quote:
Originally Posted by demarpaint View Post
Did you clean the IAC, or just adjust it? You replaced vacuum lines and then had the problem. Did you route them the exact same way? Do you have any vacuum leaks now? Did you put a vacuum gauge on it after the vacuum line replacements? Did you check for codes, even if you have no CEL? Did a vacuum line pop off? Tossing out ideas in no particular order.

Its been a while, does your TPS need to be adjusted? If so that can cause problems too.
First off, this stuff is all new to me. So if I sound ignorant, its because I indeed am....

Did you clean the IAC, or just adjust it?
Dont know what I would clean on the Idle Air Control if i replaced the whole unit. It just plugs in. It has an adjustment screw on it. The one that came with it was way too long. I used the one out of the old one and it is turned all the way in.

You replaced vacuum lines and then had the problem. Did you route them the exact same way? Do you have any vacuum leaks now? Did you put a vacuum gauge on it after the vacuum line replacements?

I was very meticulous about this. Spent a lot of time tracing them and using the correct diagram. I have gone back and double checked them all. Some were broken or routed wrong to begin with. I unfortunately, dont have a vacuum gauge.

Did you check for codes, even if you have no CEL?
Dont have a scan tool for this vehicle. Maybe I should try to get one.

Its been a while, does your TPS need to be adjusted? If so that can cause problems too.
Didnt realize this had adjustments. Didnt see anything on it that looked adjustable.
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Old 03-17-2017, 11:54 AM   #6
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With regard to the IAC, I thought you adjusted it down, re-reading I see you replaced it. Was it crusted with carbon, including the port on the engine where it sits? If so you might want to clean the port out with some carburetor cleaner.

TPS- As I said its been a while since I replaced one on an engine that old. From digging a little deeper it looks like yours is a direct replacement, some of the older Fords had to be tweaked [for lack of a better term] after installing them. You can test it with a volt meter to see if it is operating properly. Lots of how to info on the web. After market TPS can be hit or miss at best, so if you went with an aftermarket part I would check to be certain it is operating properly. Same for the IAC.

If you plan on doing your own work a code reader would be a good tool to have. A vacuum gauge is another good tool, and they aren't very costly.

Kudos for trying, and asking questions! You'll save a ton of money.

Good luck! HTH
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Old 03-17-2017, 06:48 PM   #7
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Your TBI has an idle speed actuator (ISA) which is similar to an IACV. Also, a code reader won't do you any good in a Jeep before 1996/97. You need an expensive, outdated scan tool. I don't even know if the 89 Jeeps have check engine lights.

Look at the thread linked below. There is a video a few posts down. Do your symptoms match these?
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Build thread for OJ, my YJ. 1993 Wrangler S 2.5L/AX-5/NP231, Spartan Locked Dana 30/open Dana 35 @ 4.10, 2.5" OME HD springs and Rancho RS5000 shocks, Barricade 9500 winch, custom front and rear bumpers, 136 amp alternator, 30" General Grabber AT2 tires.
1990 Yamaha TW200.

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Old 03-20-2017, 02:48 PM   #8
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Quote:
Originally Posted by MudMagnetYJ View Post
Your TBI has an idle speed actuator (ISA) which is similar to an IACV. Also, a code reader won't do you any good in a Jeep before 1996/97. You need an expensive, outdated scan tool. I don't even know if the 89 Jeeps have check engine lights.

Look at the thread linked below. There is a video a few posts down. Do your symptoms match these?
are you talking in your build thread. didnt see a video?
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Old 03-20-2017, 05:09 PM   #9
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Just a shot in the dark...

Before or after you replaced the IAC did you disconnect the neg battery terminal?
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Old 03-20-2017, 06:23 PM   #10
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Quote:
Originally Posted by michanecash View Post
are you talking in your build thread. didnt see a video?
No... Guess it didn't post... I'll look for it again and post if I find it.

Good question on battery disconnect, I'm not sure if the TBI Jeeps have good circuit protection...
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1990 Yamaha TW200.

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Old 03-20-2017, 06:25 PM   #11
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Build thread for OJ, my YJ. 1993 Wrangler S 2.5L/AX-5/NP231, Spartan Locked Dana 30/open Dana 35 @ 4.10, 2.5" OME HD springs and Rancho RS5000 shocks, Barricade 9500 winch, custom front and rear bumpers, 136 amp alternator, 30" General Grabber AT2 tires.
1990 Yamaha TW200.

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