Another High Idle Question

[Skees]

Hello everyone,

So I have a 97 Sahara that’s giving me a high idle problem. The truck just rolled over 44k miles.

In SoCal we’ve been having a lot of rain lately and my kids have wanted to go running through the big puddles, so that’s what we did! A few weeks ago, during the rain and before the puddles, I had a code P0138 thrown and I had cleared it to see if it would come back. It randomly came back a few days ago and I had cleared it one more time. It hasn’t come back since. I ordered a new Denso up and down stream O2 sensor and I’m waiting for my upstream sensor to show up but I have the down stream sensor. I couldn’t find the NGK/NTK sensor anywhere and had seen the some had luck with the Denso sensor which is why I went ahead and ordered those.

A few days ago, we went through some “deep” puddles (probably came up to the sliders) and after that I’ve been having a high idle (anywhere from 1,500-2,250) and I can’t figure out why it’s still persisting. I did a lot of searching on the forums and I took my entire throttle body assembly off and cleaned it including the IAC. They were both filthy so they definitely needed a cleaning. I even took the TPS off and cleaned everything out of there but it wasn’t dirty, especially in comparison to the IAC/TB. After cleaning the IAC out I left the intake off and did what @Jerry Bransford recommends and sprayed throttle body cleaner into the IAC inlet as well to ensure it was properly cleaned out. I couldn’t disassemble the entire IAC housing so I figured I’d go that route instead.

I also had been noticing that over the last couple months I’ve been getting a strange idle surge when I turn the heater on, but from what I’ve read that’s “normal”? Like the fan clutch engaging and disengaging is what causes the surge?

The truck is definitely due for a complete tune up and I just went to O’Rileys and grabbed a bunch of things to do the fluid flush (new coolant, PS fluid, DOT3 brake fluid, gear oil for the front/rear diffs, new spark plugs, valve cover gaskets to help isolate a small oil leak I’m having). I noticed the truck is low on coolant but I don’t think I have a head gasket issue or anything, I’m assuming my Dad might’ve tinkered with something and that’s why it’s low.

I’m thinking my TPS must be going out from the puddle splashing but I want to be sure before I go spend another ~$100 on a TPS and it doesn’t solve my problem. No CEL at all but I’m wondering how I can be 100% sure it’s the TPS before buying another one. Any help would be greatly appreciated!

 

[Skees]

Also wanted to add I have sprayed carb cleaner near the vacuum lines to see if that changes the idle, and it didn’t. I sprayed both breather valves on the valve cover, I sprayed the IM area as well as any of the other vacuum lines I could see from the engine bay. When the heater is on and the idle surges I can hear it gasping through the intake (which is a K&N intake system and I know I need to replace this with the stock intake setup, I’ve been keeping my eyes peeled for any local ones to swap with).

One thing I did notice is that I don’t have a gasket between my TB and IM, I’m not sure if that’s normal or not or if it’s something I need to buy and install?

 

[Jerry Bransford]

Also wanted to add I have sprayed carb cleaner near the vacuum lines to see if that changes the idle, and it didn’t. I sprayed both breather valves on the valve cover, I sprayed the IM area as well as any of the other vacuum lines I could see from the engine bay. When the heater is on and the idle surges I can hear it gasping through the intake (which is a K&N intake system and I know I need to replace this with the stock intake setup, I’ve been keeping my eyes peeled for any local ones to swap with).

One thing I did notice is that I don’t have a gasket between my TB and IM, I’m not sure if that’s normal or not or if it’s something I need to buy and install?

A gasket is normal between the TB and intake manifold. Does the engine rev higher/stumble if you spray something at the base of the throttle body indicating it's not air tight?

 

[Skees]

A gasket is normal between the TB and intake manifold. Does the engine rev higher/stumble if you spray something at the base of the throttle body indicating it's not air tight?

There is no change in the higher idle by spraying the base of the TB, so far the only thing that I’ve found that changes the idle is turning the heater on like I mentioned before and that just makes it surge every few seconds.

I’ll probably buy the gasket and install it anyways just to return it to somewhat normal. I was confused when I first took it off that it was a metal to metal interface like that. I was kind of hoping that it was leaking from the TB base because that would be an incredibly easy fix .

 

[Jerry Bransford]

There is no change in the higher idle by spraying the base of the TB, so far the only thing that I’ve found that changes the idle is turning the heater on like I mentioned before and that just makes it surge every few seconds.

I’ll probably buy the gasket and install it anyways just to return it to somewhat normal. I was confused when I first took it off that it was a metal to metal interface like that. I was kind of hoping that it was leaking from the TB base because that would be an incredibly easy fix .

Good plan. Just be careful to not overtighten the screws holding the TB to the aluminum intake manifold. It's not hard to strip the threads in the aluminum.

 

[macleanflood]

You mentioned HVAC issues...leads me to think you might have a vacuum line issue. Might want to cap off the HVAC line at the intake manifold or as suggested spray carb cleaner on the lines.

-Mac

 

[GregBelleville]

Good plan. Just be careful to not overtighten the screws holding the TB to the aluminum intake manifold. It's not hard to strip the threads in the aluminum.

Oof this is no joke ask me how I know... (Edited) 9 ft-lbs, no more!

 

[Skees]

You mentioned HVAC issues...leads me to think you might have a vacuum line issue. Might want to cap off the HVAC line at the intake manifold or as suggested spray carb cleaner on the lines.

-Mac

I’ve sprayed all of the visible lines in the engine compartment and it didn’t seem to affect anything, I sprayed the entire line as well not just at the ingress/egress points.

I’m curious if there’s a fool proof way I can test the TPS so I can see if I’m headed in the right direction. I’ve also double and triple checked to make sure everything was seated properly and the connectors weren’t pushing through the rear causing the issue.

The fact that this happened after running through a puddle makes me wonder if I did in fact mess up the TPS I just don’t want to spend ~$100 on a sensor for it not to solve the problem.

 

[Skees]

Oof this is no joke ask me how I know... 9 ft lbs, no more!

Noted! Thank you very much and I’ll be sure to keep that in mind when I get the TB gasket to install.

 

[Jerry Bransford]

Oof this is no joke ask me how I know... 20 ft lbs, no more!

Actually it's only 9 ft-lbs aka 108 inch-lbs. 20 ft-lbs would probably strip the threads. Use nothing bigger than a 3/8" torque wrench for anything that low. And @Skees

 

[Skees]

After doing some more thinking I’m going to try and crawl under the truck and look around and see what’s going on. No CEL makes me think that maybe it’s not the TPS and that it must be a vacuum leak somewhere… Thank you for those torque specs @Jerry Bransford i really appreciate that!

 

[GregBelleville]

Actually it's only 9 ft-lbs aka 108 inch-lbs. 20 ft-lbs would probably strip the threads. Use nothing bigger than a 3/8" torque wrench for anything that low. And @Skees

View attachment 502629

Yep, not sure why I thought it was 20 ft lbs, thanks for keeping me honest, maybe that's how I ended up in that mess in the first place.

 

[TJuser]

Yep, not sure why I thought it was 20 ft lbs, thanks for keeping me honest, maybe that's how I ended up in that mess in the first place.

Yeah no I tried 20 ft/lbs mounting a turbo to the pedestal...strips it out far too easy.

kids, righty loosey happens too easy with aluminum

 

[Skees]

Well I took the truck for a drive and the CEL came back on. This time with 2 codes; P0123 and P0138 (I’ve seen the P0138 code before and bought new O2 sensors because of it). Looks like the TPS is going then?

Also something worth noting is I have noticed some noise coming from the wheel when turning which is now making me think my clock spring is going bad and that’s what the actual culprit is here .

 

[Skees]

I just wanted to update this thread as I have solved my problem!

I ran up to Orileys this evening and grabbed a new throttle body gasket to replace the non-existent one. So that is rectified. I also swung by NAPA and grabbed an Echlin TPS to install. My downstream O2 sensor showed up as well so I had everything needed to test all my theories out.

Started off with the TPS, upon removal of the “dead” one I noticed it did not have a seal on it at all. Which makes me believe this isn’t the OEM sensor. I can attach some pictures but this makes way more sense why the TPS would’ve died from a puddle, no seal + water = bad time. So I got the new one installed with the seal and I installed the throttle body gasket when I put everything back on.

Finished up by doing O2 sensors, quick and easy.

Did the ECM reset (positive and negative leads held together for 30+ seconds) and hooked everything back up. She fired right up and is purring like a kitten! Idle problem solved!