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Ballast Resistor question?

T

The Lure Washer

NAXJA Forum User
Location
Bristol, CT
Can a ballast resistor suffer from thermal failure. My 1990 has an issue where the rpms creep up to around 1100 from 500 at idle. This only happens when the engine is hot. When it does creep up the minute I touch the gas it will stall or attempt to. When it does that if I remove my foot fast enough it will stay running. When It does restart the ropms shoot up to around 3500rpm. I initially thought that this could have been a fuel pump issue. So I replaced that. and Just about everything else Under the hood with the ecception of the fuel injectors, MAP and MAT sensors and the Ballast resistor.
 
you can bypasss the resistor and see if anything changes,but i doubt it has anything to do with your prob its pretty much a works or dosent type part
 
Hi,
I doubt it's the ballast resistor but You might want to look at your IAC (Idle air control valve) this controls the idling speed. Over time they become gunged up and sticky, I did manage to take mine apart and clean it and I'm no genius, just be careful. Hope this helps.
 
Jeepcreep said:
Hi,
I doubt it's the ballast resistor but You might want to look at your IAC (Idle air control valve) this controls the idling speed. Over time they become gunged up and sticky, I did manage to take mine apart and clean it and I'm no genius, just be careful. Hope this helps.
Click to expand...

X2 on the IAC.

Take it off and clean it. Better yet, remove the trottle body, carefully dismantle it and clean everything with break cleaner. A new IAC would not hurt either although I have not replaced mine. I just clean everything and replace...
 
I think your dealing with a vacuum leak. Check all the bolts on the TB and intake, all vac line connections, etc. You can use a can of spray carb cleaner to shoot at obscure areas - if it rev's up, you have a leak.
 
Just curious if the TPS is functioning correctly.
 
Fuel pressure was 32lbs before the new pump went in. Fuel pressure regulator and TPS are new. I did find that the 2 vacuum lines that go from the little tower on the Intake manifold to the vacuum line tree had some heater hose that was all dry rotted that the PO must have used instead of actually fittings. I replaced those and the stall has stopped but I have a high idle now. Its about 900 in drive and about 1500 in park.
 
You can change the base idle screw setting at the throttle body housing, just be sure to check/adjust the TPS when done. I believe the screw is 3/32 allen.
 
Fully warmed up and idling in Park I think you are looking for a 750 rpm base idle.
 
joe_peters said:
Fully warmed up and idling in Park I think you are looking for a 750 rpm base idle.
Click to expand...

Correcting myself, should be about 700-800 RPM, in drive. You need a second person to sit in the vehicle and apply the brakes--DO NOT trust the parking brake to hold it.
 
joe_peters said:
Correcting myself, should be about 700-800 RPM, in drive. You need a second person to sit in the vehicle and apply the brakes--DO NOT trust the parking brake to hold it.
Click to expand...

That reminds me of when I was younger and dumber. When I was 18 or so, I was working on my 1969 Ford pickup. I was tuning the carb with it idling in drive, parking brake set, no other wheel chocks. It took a while to tune, so I naturally forgot about the current setup. It was running pretty good so I decided to give it a good rev by working the throttle valve on the carb by hand. I got lucky, but it sure scared the crap out of me. Now I try to keep my head a little further out of my ass for safety reasons.
 
I've had a TPS mess with my idle (went way high at start up after a motor wash), loose intake manifold bolts (when it got hot the idle went up), IAC was sticky (it was the OEM original 20 years old and the grease inside of the IAC was the consistency of plumbers putty) gave me odd and random idle issues.
The last problem turned out to be a bad ground splice in the harness for the TPS on the firewall. It rarely idled the same RPM twice, seemed worse after it heated up (closed loop).
Just for a test you could hook up a temporary ground to the chassis from the TPS and see what happens or do an ohm test on the ground circuit and maybe shake the harness.
I've run good ballast resistors, marginal to bad ballast resistors and jumped ballast resistor and have never noticed any appreciable difference in idle. The marginal ballast resistor would mess with my mid to high RPM though, it would occasionally starve for fuel at higher RPM's while driving.
 
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