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90 Renix AX15, slightly high idle...

S

skyb44

NAXJA Forum User
Location
Fort Collins Colorado
I've done a fair bit of troubleshooting so here's the story


1000 rpms on startup
1200-1250 warm (consistent)
good throttle response, decent gas mileage (17-20)
the 1250 rpm occurred after cleaning the throttle body, previously tended to be around 1000 warm, which i would still consider on the high side of normal.

checked-
function of IAC- I threaded the plunger in, reinstalled without the connector- idle was initially high (2000) plugged back in, IAC reigned it back in to 1200 rpms again.

looked for vacuum leaks using the "spray carb cleaner at your vacuum lines and listen for a change in idle" trick.

coolant temp sensor under exhaust manifold seems good- 600 ohms warm
air temp sensor in intake manifold also reads around 600 ohms warm

TPS is at 17% of reference voltage per maths/volt meter.

About the only thing i can think is that the IAC is getting stuck before it can fully close off the idle passage.

I suppose vacuum leaks are still a possibility as this jeep is old as dirt (though in good shape) some of the lines look kind of rough.
 
I plug up all the vacuum holes in the intake manifold when I have high idle issues, with short pieces of tubing with a screw or bolt in the end. It will run just fine with all of them plugged except the fuel regulator vacuum line(and the vacuum line to the TB from the MAP snsor). And see if my idle changes.

1200 RPM is about what you get when one of the smaller vacuum lines is open. Check the large vacuum line running to the vacuum canister behind the right front bumper. That vacuum line has a tenancy to rot under the battery tray. The vacuum canister mounting tabs have a tenancy to break off and the canister kinds of bangs around behind the bumper and the vacuum lines come loose. One of the first signs of the vacuum canister problems, is your heater acting up, it only throws heat at higher RPM's.

Re torque the manifold bolts from the center out, top and bottom, If I remember correctly the books says right around 25 ft lbs, so don't over tighten. Check the book to make sure my memory is correct and make sure of the tightening sequence.

The end studs on the exhaust manifold snap off real easy. soak in penetrating oil before even going near those.
 
I wonder if someone messed with the throttle butterfly stop screw at one time.......

Cruiser’s Renix Throttle Body Butterfly Adjustment
Okay. Let's start from scratch. First off, that's not an idle adjustment screw. It's a throttle butterfly stop screw. It's purpose is to allow the butterfly to be as close to completely closed as it can be without binding or wearing into the throttle body. It was never intended to be adjusted in the field. But, Uncle Bob didn’t know that, did he?

Engine off. Back off the butterfly stop screw with a 3/32" allen wrench until the butterfly is completely closed. Now. turn the screw in until the FAINTEST movement of the butterfly opening is detected. This can be done more easily with the throttle body removed. If you remove the throttle body, be sure to replace the gasket underneath it after thoroughly cleaning the old one off.
Revised 07/07/2012
 
1. What TRANSMISSION?

2. Manual transmission, in neutral, after 20 minutes of operation idle should be 700-750 RPM. Automatic transmission, in DRIVE--parking and service brakes applied--after 20 minutes of operation should be 700-750 RPM.

3. Have you checked the throttle plate shafts for leakage? A little silicon at each end will temporarily seal any leaks for testing, or you can use kid's play-doh, etc.
 
joe_peters said:
1. What TRANSMISSION?

2. Manual transmission, in neutral, after 20 minutes of operation idle should be 700-750 RPM. Automatic transmission, in DRIVE--parking and service brakes applied--after 20 minutes of operation should be 700-750 RPM.

3. Have you checked the throttle plate shafts for leakage? A little silicon at each end will temporarily seal any leaks for testing, or you can use kid's play-doh, etc.
Click to expand...

Op's title says ax15...
 
cruiser54 said:
I wonder if someone messed with the throttle butterfly stop screw at one time.......

Cruiser’s Renix Throttle Body Butterfly Adjustment
Okay. Let's start from scratch. First off, that's not an idle adjustment screw. It's a throttle butterfly stop screw. It's purpose is to allow the butterfly to be as close to completely closed as it can be without binding or wearing into the throttle body. It was never intended to be adjusted in the field. But, Uncle Bob didn’t know that, did he?

Engine off. Back off the butterfly stop screw with a 3/32" allen wrench until the butterfly is completely closed. Now. turn the screw in until the FAINTEST movement of the butterfly opening is detected. This can be done more easily with the throttle body removed. If you remove the throttle body, be sure to replace the gasket underneath it after thoroughly cleaning the old one off.
Revised 07/07/2012
Click to expand...


This man gets the prize- some jackass previous owner moved the throttle stop screw. I had overlooked this because I couldn't figure out what tool it took and I figured given my luck it must be something more complicated.

As a small correction to this guide- on my jeep anyway, the screw takes a 2.5mm allen wrench. 3/32 will work in a pinch but is loose. I am now running an even 750 RPM with it warm (150F on the gauge right now)

I did check to make sure the screw was contacting the throttle linkage using a piece of foil as a gauge, i also used the foil to make sure the throttle plate was not contacting the inside of the body. My best guess is someone did this to compensate for a very dirty throttle body at some point.

I'll have to see how much gas this saves me in ridiculous front range colorado stoplight traffic.
 
skyb44 said:
This man gets the prize- some jackass previous owner moved the throttle stop screw. I had overlooked this because I couldn't figure out what tool it took and I figured given my luck it must be something more complicated.

As a small correction to this guide- on my jeep anyway, the screw takes a 2.5mm allen wrench. 3/32 will work in a pinch but is loose. I am now running an even 750 RPM with it warm (150F on the gauge right now)

I did check to make sure the screw was contacting the throttle linkage using a piece of foil as a gauge, i also used the foil to make sure the throttle plate was not contacting the inside of the body. My best guess is someone did this to compensate for a very dirty throttle body at some point.

I'll have to see how much gas this saves me in ridiculous front range colorado stoplight traffic.
Click to expand...

It was "Uncle Bob"--he can't keep his fingers off things.
 
Post number one says:

coolant temp sensor under exhaust manifold seems good- 600 ohms warm
air temp sensor in intake manifold also reads around 600 ohms warm
Click to expand...

The CTS reading should be a good bit lower than the intake air temp sensor!!!!! I have no idea what temp "warm" is?
 
Ecomike said:
Post number one says:



The CTS reading should be a good bit lower than the intake air temp sensor!!!!! I have no idea what temp "warm" is?
Click to expand...

I could be a little off on those numbers- I was basically looking for a short or an open circuit.

Seeing how it runs well and has decent fuel economy I'm not going to mess with it.
 
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