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Topic: low idle (Read 1854 times) previous topic - next topic

low idle

hey everybody, was wondering how to raise my idle up a couple hundred r.p.m.'s. i have an 86 cougar with the 3.8. i'm the original owner and i'm familiar with older engines without computers. i tried following the chilton and haynes manuals on this idle thing but they are no or of little help. i had the vacuum lines checked and repaired as necessary. all sensors are new as well as the e.g.r. assembly. also the idle position unit is new. adjustment of this idle unit is quite a puzzle. one manual has a way of adjusting it, but i don't understand what there talking about....way too confusing. need something in layman terms. about ten years ago a mechanic raised the idle and said to drive it awhile so the computer can learn the new settings ...sure enough it got better. he's gone...and i got low idle. also when idling...if you give the accelarator pedal a good shot and let off real quick the engine idle goes real low, like a couple hundred r.p.m. just for a second..then back to normal low idle. thanks in advance for any help. oh yeah the mileage on the car is 110,000. miles...in good shape and well cared for.

Re: low idle

Reply #1 –
hows it going.First try cleaning the throttlebody with carb cleaner. Then you have to follow the procedure for idle setting.Its a little lenghty but fords are critical about it

Re: low idle

Reply #2 –
Your idle speed is controlled by the Electronic Engine Control (EEC).
The EEC does this by controlling the Idle Speed Control (ISC) motor.

Have you ever run the engine with the air cleaner off and watched the ISC to see if the plunger ever moves?

There are two adjustments.
1. The idle stop adjustment screw. This is on the side of the throttle body and difficult to get at without pulling the throttle body. the screw is designed to never be fooled with. It is self locking with no head on it for using a tool. You have to get on it with pliers.
If you think it has been moved and want to adjust it I recommend pulling the throttle body and replacing the 5mm x 0.80 screw.

Adjustment: With the throttle plates closed turn the screw in until you have a .005" gap then turn it in 1 1/2 more turns. You may want to put something on the threads to keep it from moving.

2. Position the ISC motor.
Remove the air cleaner. Notice where the ISC plunger is. Install a jumper wire on the self test connector from signal return to the STI pigtail connector. (This is the same jumper you put on to pull codes.)  Turn the key on don't start. The ISC plunger should retract.
Turn the key off. The gap between the ISC plunger and the throttle lever should be 7/32". Use a drill bit for a feeler gauge.
Adjust by loosening the ISC mounting screws and turning the long adjusting screw under the ISC. The one with the spring on it.

When the adjustments are correct, if you still have the problem get back to us and we will go from there.

Re: low idle

Reply #3 –
thanks i'll try it

Re: low idle

Reply #4 –
am looking at the connectors....i know which one is the signal return pin, but not the single input connector(sti pigtail)...chilton manual on page 100 has a similar description of idle adjustment.....i'll keep looking

Re: low idle

Reply #5 –
The STI is a single wire by its self. Not part of the six pin self test connector. It is located in the same area you found the six pin connector.

Re: low idle

Reply #6 –
thanks.....i'm on it.....i'll let you know what happens tomorrow.

Re: low idle

Reply #7 –
did it...drove around 50 miles today...idles smoother and just a tad higher...still low. i noticed when i push and hold down the brake pedal the idle goes lower, let off the brake pedal and idle goes back up. this is when tranny is in "drive". in neutral, the idle is smooth....the nuetral idle is what the drive idle should be. with the a/c/on that is. in short ....with a/c on and in drive at a red light the idle is about 500-550 r.p.m.'s. in park or neutral the idle is about 550-570 r.p.m.'s. if i move the sliding a/c contrrol to vent or max or floor the idle goes up to 650 r.p.m and down again. i feel there is a vacuum leak at my brake booster or tied into it somewhere. i'll keep looking. oh yeah to add insult to injury, my a/c now blows out the floor and top vents now..not the dash vents....maybe its all tied together somehow...lol....any help would be appreciated.

Re: low idle

Reply #8 –
My T-Bird doesn't have a tach so I dug out my old dwell/tachometer from the obsolete tools bin.
It didn't work anymore. Took it apart and found a wire that had pulled loose. Never properly soldered in the first place.

Anyhow, here is what I see on my car:
Idle, park, no a/c, no brake  800 rpm.
Idle, park, no a/c, brake      750 rpm
Idle, park, A/C,. no brake    700 rpm clutch 900 rpm no clutch.
Idle, park, A/C, brake          650 rpm clutch 850 rpm no clutch.

Idle, drive, no A/C, brake    630 rpm.
Idle, drive, A/C, brake        530 rpm clutch  680 rpm no clutch.

My A/C short cycles because the freon is low. There is not any time for the rpm to settle down between clutch and no clutch.

My decal says the idle in drive should be 500-600 rpm.

My vacuum in park  no A/C is 18.5 inches of mercury and drops to 18 with brake.
 My car idles smooth at the lowest speeds.

When I took the cap off an unused port on the vacuum distribution manafold the idle speed increased. Disconnected and capped or clamped off all the vacuum lines I could find. Trying to find the vacuum source for the heater-A/C control. Never found it.
One line I disconnected and capped off caused the idle to drop way down and run real rough. I suspect it goes to the MAP sensor.

Is rough idle your problem? You seem to be within the specs but on the low end.
 

Re: low idle

Reply #9 –
thanks softtouch...no my idle is quite smooth in park or neutral. only when i push on the brake pedal with a/c on does it go too low. have my radio and a/c heater control panel and instrument panel off the car. am trying to get at one of the vacuum canisters behind the instrument panel. want to apply vacuum to it to see if it works. if it works then i should get air out the dash vents. ican kinda live with the low idle, but this  a/c problem is killing me. i think its tied together. its a long shot, but i just have a feeling about it. its funny that the idle is not affected when my a/c is off and i apply the brakes.....only if the a/c is on do i have a problem. well i'll going back outside to try to finish up.....the heats killing me...am in florida...lol...need the a/c...

Re: low idle

Reply #10 –
oh yeah one more thing...my timing was 5 degrees off...it's on the money now....same thing....lol..

Re: low idle

Reply #11 –
good news...the problem with the a/c not blowing thru the vents was the vacuum line from the tree in engine compartment on drivers side. my car has seven nipples for vacuum on the tree. the a/c heater control source is the second one down on the passenger side. there must be no leaks what so ever. it's critical. the line ford uses is ultra thin and plastic not rubber. now my selector switch works like butter...of course i lubed everything prior. i may change all my vacuum lines in the engine compartment to rubber hoses. the lower than normal idle i'll fix by changing that screw under the throttle body to one that can be adjusted...there's a post of this fix in the archives. well i hope this helps someone get there air fixed. i'll put my car back together tommorow...too tired now.  thanks for all your help. it's nice to know we're not alone out here when we run into problems..see ya later