Idle slowly climbs - what could it be

[robplus4]

Can anybody help.


My car starts & runs, but after 10 min. idle starts at 775 then slowly climbs to about 1400 rpms after about 30 seconds. I can tap the gas and it drops back to 775. that will last for about 30 seconds, then it starts climbing again.

[sdg3205]

Could be as simple as tweaking curb idle. Engine vacuum may be pulling the butterfly valve open just enough to disengage the micro switch, which would disable the idle speed motor and increase idle rpm. You may also have a vacuum leak. Is your mixture set properly?

[Bitsyncmaster]

Could be as simple as tweaking curb idle. Engine vacuum may be pulling the butterfly valve open just enough to disengage the micro switch, which would disable the idle speed motor and increase idle rpm. You may also have a vacuum leak. Is your mixture set properly?

+1

When your engine warms up the oil gets thinner and it takes less throttle to hold 775 RPM. If your curb idle (lower screw on throttle arm) is set to high, then the idle motor may be all the way closed and cannot drop the idle anymore as it warms up.

If you find that it requires that curb idle screw backed all the way out, then you may have the bad deceleration valve springs on the throttle plates. That was the problem on my car. My curb idle screw was fully backed out and it would still climb the idle to 1000 RPM after it warmed up.

[robplus4]

Could be as simple as tweaking curb idle. Engine vacuum may be pulling the butterfly valve open just enough to disengage the micro switch, which would disable the idle speed motor and increase idle rpm. You may also have a vacuum leak. Is your mixture set properly?

Curb idle is all the way down.
Mixture is set properly.
I did notice that if I engage the mico switch the problem stops, but then it fail smog.

[DMCMW Dave]

Curb idle is all the way down.
Mixture is set properly.
I did notice that if I engage the mico switch the problem stops, but then it fail smog.

Which microswitch? High speed or idle?

[sdg3205]

Curb idle is all the way down.
Mixture is set properly.
I did notice that if I engage the mico switch the problem stops, but then it fail smog.

So, you DO know what the problem is! Hah. If you are indeed pressing the idle micro switch and NOT the WOT switch and it fixes the idle issue that's at least part of the problem.

Well, you need to prioritize issues. What good is passing smog if the car isn't running properly? Get the idle set properly, confirm mixture with a dwell meter and then figure out what the issue is with smog. Me thinks if it fails smog at idle the mixture isn't set right or your cat is toast.

[robplus4]

Which microswitch? High speed or idle?

High speed.

[Bitsyncmaster]

High speed.

The only thing the wide open throttle switch does is run the frequency valve at 60% duty cycle. So if your are running closed loop adjusted properly, it would run the engine richer.

[robplus4]

The only thing the wide open throttle switch does is run the frequency valve at 60% duty cycle. So if your are running closed loop adjusted properly, it would run the engine richer.

I'm sorry, close loop?

[sdg3205]

Closed loop means the lambda system (mixture and emissions system) is functioning to spec.

[Bitsyncmaster]

Closed loop means the lambda system (mixture and emissions system) is functioning to spec.

+1
Closed loop is more of a term we use in electronics. When the lambda ECU is controlling the frequency valve (FV) to open an amount based on the values provided by the oxygen sensor (O2) it is considered closed loop because if one of those devices fails it stops varying the frequency valve.

When one device fails or the wide open throttle (WOT) switch is pressed or the O2 sensor has not heated up yet, the FV is opening at a fixed rate. Hence something has opened the loop.

[sdg3205]

Rob (I suspect that is your name!)

Are you sure your mixture is set properly? Have you confirmed with a dwell meter?

Often when an owner or shop doesn't know how to adjust k-jet, they run open loop and really rich up the mixture. I think this would cause it to fail smog at idle. Another possibility is the lambda system isn't operating because it isn't getting power. Can you confirm it is? When I first got my car it ran very rich to compensate for an inoperable lambda system dude to a relay pin backing out.

[robplus4]

Closed loop means the lambda system (mixture and emissions system) is functioning to spec.

Update:
I replaced the fuel injectors.(picked them up from Rock auto online)
No more smell, idling fine now, and it passed smog.

Thank you for all you help.

Robert
Temecula, Ca