Novak Conversions Jeep Wrangler TJ engine mounts

High idle in park & neutral. RPM's jump when going over bumps.

Wherna491

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May 27, 2023
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California
High idle in park & neutral. RPM's jump when going over potholes while drving. The idle at start up is around 1500, will randomly do it at startup does not happen all the time. I have replaced o2 sensors, crank sensor, map sensor, tps sensor, and IAC. All parts are OES parts by NTK. I have not found a vacuum leak, removed battery & inspected vacuum reservoir no cracks present. Sprayed all vacuum elbows & vacuum lines, no chnage in rpm. I checked intake & exhaust manifolds bolts & nuts, all are tight. Sprayed brake clean on anything possible, still no luck. I live in an area where it gets above 110 in the summer, randomly while driving I would get no airflow out of vents but you can hear the blower motor. I did notice slack on my throttle cable and plstic broken on it, can this be related to my symptoms?
 
tj throttle.JPG
 
I unplugged my brake booster and plugged in a cheap one I bought on Amazon.

Found the throttle body gasket leaking and I probably need to o-ring the throttle body.

-Mac
 
Your hvac door actuators are vacuum operated. If you lose air out of your vent, it’s defaulting to the defrost mode because you have a vacuum leak. Two common sources are the elbow on intake below the throttle body which is the source for the HVAC vacuum as well as below the battery there is a vacuum reservoir.
 
I unplugged my brake booster and plugged in a cheap one I bought on Amazon.

Found the throttle body gasket leaking and I probably need to o-ring the throttle body.

-Mac

Did you have to block the exhaust?
Will be buying a smoke tester, will reach out with results hopefully soon!
I unplugged my brake booster and plugged in a cheap one I bought on Amazon.

Found the throttle body gasket leaking and I probably need to o-ring the throttle body.

-Mac

Found my leak! Smoke is coming out of throttle shaft, shaft has excessive play.
 
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Im afraid you’re going to need to keep looking. The throttle shaft leak is above the MAP sensor and will have a lesser affect than what your experiencing. The MAP sensor is blind to air infiltration downstream of it. That’s where you should be looking.
 
Im afraid you’re going to need to keep looking. The throttle shaft leak is above the MAP sensor and will have a lesser affect than what your experiencing. The MAP sensor is blind to air infiltration downstream of it. That’s where you should be looking.

I get your point, but if I introduce positive pressure from the leak to the negative pressure I should see a change in rpms right? I mean its technically getting unmetered air introduced, Will still replace throttle body as its obviously got a decent leak and the shaft does have a good amount of play.. I'm not sure how to post videos on here, but will update after I replace throttle body
 
Did you inspect the hard plastic HVAC line from the intake elbow to the firewall? Mine had worn through where it passed behind the PCM on the way to the reservoir. It has two one way check valves that need to be considered if your smoking this line. I also want to correct the statement above regarding the MAP. It will see changes in air leaks or changes to the vacuum downstream. MAF will not, (Chevy guy - old habits die hard). If your idea is linked to your vacuum leak, it’s bigger than the throttle shaft. I also have the throttle shaft leak with the smoke test (many others do as well) but it has no affect on idle. Don’t want to see you needlessly spend money on a TB.
 
Did you inspect the hard plastic HVAC line from the intake elbow to the firewall? Mine had worn through where it passed behind the PCM on the way to the reservoir. It has two one way check valves that need to be considered if your smoking this line. I also want to correct the statement above regarding the MAP. It will see changes in air leaks or changes to the vacuum downstream. MAF will not, (Chevy guy - old habits die hard). If your idea is linked to your vacuum leak, it’s bigger than the throttle shaft. I also have the throttle shaft leak with the smoke test (many others do as well) but it has no affect on idle. Don’t want to see you needlessly spend money on a TB.

I removed the battery and put the vacuum reservoir on top the battery. I had cleaned the box and inspected for any obvious cracks on resevoir and vacuum line, no cracks were present. I had the engine running and sprayed all lines & vacuum reservoir with brake cleaner and moving the lines, no sudden change in rpm. I have been trying to duplicate the high idle in park & neutral, have not been able to do it for the past week. I only have the rpm spike when hitting bumps or dips on the road at speeds above 35. Will smoke the exhaust when I get a chance. I did not find any leaks from any vacuum lines. As for the check balls on the vacuum line, how would you inspect & check them.
 
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Did you inspect the hard plastic HVAC line from the intake elbow to the firewall? Mine had worn through where it passed behind the PCM on the way to the reservoir. It has two one way check valves that need to be considered if your smoking this line. I also want to correct the statement above regarding the MAP. It will see changes in air leaks or changes to the vacuum downstream. MAF will not, (Chevy guy - old habits die hard). If your idea is linked to your vacuum leak, it’s bigger than the throttle shaft. I also have the throttle shaft leak with the smoke test (many others do as well) but it has no affect on idle. Don’t want to see you needlessly spend money on a TB.
So I ended up smokiing the line after the check valve that goes to hvac unit, had the smoke coming out the hvac unit. Is that common, and will it cause my high idle? I will be removing the throttle body and cover opening to re-smoke the system in hopes I find something.
 
Not common and yes, will cause the idle. Unplug the HVAC at the firewall and seal it off with a plug and see if you "fix" the issue.

-Mac
 
Not common and yes, will cause the idle. Unplug the HVAC at the firewall and seal it off with a plug and see if you "fix" the issue.

-Mac

This things kicking my ass... I replaced hvac control unit, still have the random high idle in neutral & park & rpm jump at speeds above 40mph when hitting bumps. I removed throttle body and covered the opening to perform smoke test once again. I was moving all parts that can affect vacuum, only found very little smoke coming from rear pcv elbow. I recently replaced the elbow 8000 miles ago. I'm stuck between a possible throttle cable sticking or its just the rear pcv elbow
 
Novak Conversions Jeep Wrangler TJ engine mounts