Rough idle again.
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Joined: Nov 2006
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Rough idle again.
I cleaned my throttle body and my van was running better, but the rough idle is coming back, could i have a bad throttle position sensor? I had auto zone do a scan,and no codes were found. I have a 94 aero with a 3.0 liter Also noticed my temp gauge always moving either dead center or close to cold ,could that sensor affect idle?
Last edited by alanjones; Dec 29, 2006 at 08:24 PM.
Former ******
Joined: Nov 2004
Posts: 4,901
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From: Salt Lake City, Utah
I would not suspect the TPS, but the idle air control may be gumming up again. Best policy is to replace it with a new one if cleaning it a second time does not help, or the problem returns again.
Lead Driver
Joined: Sep 2003
Posts: 7,016
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From: SoCal
You can check the TP sensor pretty easily using a multimeter. It's just a fancy variable resistor; there is a wiper terminal and the two ends of a resistor. You can disconnect it from the harness and measure across two of its terminals. If moving the throttle doesn't change the readings, move one of the multimeter probes to another terminal. The resistance should change smoothly with the throttle motion. If it jumps or stutters, it probably should be replaced. Obviously, this is much easier to see on an analog meter.
You can also check the idle air bypass valve by disabling it. The idle will drop, and you can bump it back up by turning the idle stop screw. At that point, if your idle is still rough, it's not the valve. (Restore by turning the screw back down, and reconnecting the valve.)
The temp gauge uses a different sensor than those used by the EEC for engine operations.
You can also check the idle air bypass valve by disabling it. The idle will drop, and you can bump it back up by turning the idle stop screw. At that point, if your idle is still rough, it's not the valve. (Restore by turning the screw back down, and reconnecting the valve.)
The temp gauge uses a different sensor than those used by the EEC for engine operations.
Former ******
Joined: Nov 2004
Posts: 4,901
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From: Salt Lake City, Utah
Possible, it never hurts to replace the fuel filter, though generally a plugged filter will cause performance problems as RPMs or engine load increases. A broken vacuum line or a dirty MAF can cause idle issues. Still, probably 70% or more of idle issues on Fords are dirty or gummed IAC valves. The remaining problems are a mix of plugged idle passages, dirty MAF, vacuum lines, faulty purge solenoids, misfire, ignition problems, faulty AC relays (very rare but carbon tracking inside the relay can cause issues), faulty injectors, and valve problems.
Postmaster
Joined: Apr 2001
Posts: 3,818
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I would agree with the advice above. Not likely fuel filter or TPS for rough idle problems.
Reviewing your previous posting regarding the extremely dirty throttle body makes me wonder about your PCV valve and/or associated vacuum lines. Have you checked the vacuum "tree" with all the various vacuum line connections to ensure all is tight there and any vacant ports have a plug on them? What you describe just feels more like a vacuum problem. Also check the lines from the vapor cannister to the manifold. They get brittle and can break in hidden places. Something is amiss somewhere to cause that heavy of build up in the throttle body.
Reviewing your previous posting regarding the extremely dirty throttle body makes me wonder about your PCV valve and/or associated vacuum lines. Have you checked the vacuum "tree" with all the various vacuum line connections to ensure all is tight there and any vacant ports have a plug on them? What you describe just feels more like a vacuum problem. Also check the lines from the vapor cannister to the manifold. They get brittle and can break in hidden places. Something is amiss somewhere to cause that heavy of build up in the throttle body.
Post Fiend
Joined: Apr 2005
Posts: 5,720
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From: Washington state
also look for air leak between MAF and throttle body....unmetered air will cause idle problems...also would explain the extremely dirty TB, unfiltered air
measure the fuel pressure at idle and at hwy cruise....will require a long remote FP gauge....should be min. of 30 psi at idle and steady....35 psi at cruise and steady....
another place to look for vac. leaks is the heater/ac vac. control tubes....they get pulled off accidently...break down from old age
the vapor canister line that aeroC mentioned gave me problems
measure the fuel pressure at idle and at hwy cruise....will require a long remote FP gauge....should be min. of 30 psi at idle and steady....35 psi at cruise and steady....
another place to look for vac. leaks is the heater/ac vac. control tubes....they get pulled off accidently...break down from old age
the vapor canister line that aeroC mentioned gave me problems
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Lead Driver
Joined: Sep 2003
Posts: 7,016
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From: SoCal
Heater control vacuum lines are very small, and probably will not cause idle problems when disconnected. (At least mine did not.) But if your HVAC control isn't working, that's probably a leaking vacuum line.
I'd look at the PCV valve again (in addition to all those other things others mentioned). You can pull its line out of the side of the air intake hose, and plug it with something to see if that helps with the idle.
I'd look at the PCV valve again (in addition to all those other things others mentioned). You can pull its line out of the side of the air intake hose, and plug it with something to see if that helps with the idle.
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Lead Driver
Joined: Sep 2003
Posts: 7,016
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From: SoCal
Alan,
Try plugging the hole in the inlet tube where the PCV valve went in with the engine idling, and see if that makes a difference in idle speed. If so, then maybe the PCV does need to be replaced.
Try plugging the hole in the inlet tube where the PCV valve went in with the engine idling, and see if that makes a difference in idle speed. If so, then maybe the PCV does need to be replaced.