Ideling question

archerman0531

Registered User
So, ever since I bought this car(1990 cougar xr7) it has always idled high(1500rpm for about 10-12 seconds, and that varies) and then goes down to around 1000-1100 rpm. When driving and push the clutch in it also revs higher to the 1500rpm range. How do I adjust the idle? The throttle stop screw was adjusted to were it wouldn't hit the stop. I adjusted it to where it actually rests on the stop. I don't see anything else for an idle adjustment. After its up to opp temp. It likes to elevate a couple 100 rpm and die back down and back up for a while almost like surging but not as exagerated, and finally settles down to 1000-1100. You can watch the vacuum/boost gauge waiver from 21-22 inch/lbs at 1000-1100rpm to 16-18inch/lbs as it increases in rpm.

Any help would be greatly appreciated.

I'm thinking possibly MAF, TPS, or IAC.
 
The TPS Sensor should be able to compensate some.

Very small rotation will change the voltage with I think a window of 95-120.

Do some searching and it will probably make more sense than my explanation.

Paul
 
vac leak sucking in un-metered air causing it to rev higher but it is going to cause a lean condition. I had a vac leak so bad on my SC once that it idled high and got the headers glowing red. that scared the hell out of me.
 
hmmm. i ripped mine back down to the intake manifold, resealed everything. I put teflon gaskets on the IC pipe connections, and got a new hose with some extra length for the PCV to SC plenum connection that kept popping off. After that mine idled good.
 
Well, I'll refog it and see if I can maybe come up with something, because i first believed it was a vacuum leak as well because it takes forever for the Rpms to come back down if you flip the throttle. About 4 seconded to come down from the 2500rpm, sticks at 15-1700 for about 10-15 seconds, drops down to around 1200 and slowely ideals down to the 1000 rpm. Once it hits 1000 it will stay unless you flip the throttle again and it does the exact same thing over. So I'm stuck as to what it could be. Maybe the ECM needs to have the idle rpm adjusted? I'm not for sure if that's where idle is controlled from, i know in my f150 it was.

Also the whole top end has been rebuilt in the last 700 miles. And appears to have new gaskets for the intake manifold, as well as the IC Teflon gaskets
 
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there is a value in the EEC for base idle, and it can be adjusted, but if you've never messed with it, then there's no reason to believe it has been altered. Anything from the point of the mass air flow sensor forward has no effect on idle. Anything after the mass air flow sensor will be air extra air coming in that the computer isn't compensating for by adding fuel. If it's post throttle body it will cause the engine to idle higher, or "hang" like you are describing.
 
check the lower IC tube to IC connection and tighten it up with a 13mm wrench (ratcheting wrench is a god send for the left nut on the stud). Also check the vacuum connection on the rear of the supercharger inlet plenum behind the throttle body. Check the passenger side valve cover under the throttle body where the PCV connects to this stupid plastic junction.
 
vac leak sucking in un-metered air causing it to rev higher but it is going to cause a lean condition. I had a vac leak so bad on my SC once that it idled high and got the headers glowing red. that scared the hell out of me.

X2 to this. You're pulling air from somewhere.
 
I do hope you will post when you find the problem. I've had this issue almost exactly since I bought my '91 with 61,000 miles last year. Lowered it, painted it, put wheels n tires on it, put head gaskets in it, and its now sitting under a car cover in the driveway cause ive never been able to figure it out and gave up on it. Bought a '90 with 199,000 miles on it, put head gaskets in it and drive it daily. Ready to sell the red one cause I cannot stand the idle problem. Fogged, replaced every gasket from the block up, IC tubes, intercooler, the works... I wish you the best of luck and will be watching eagerly for your fix.
 
I haven't found the problem yet. My guess is a sensor. I know all vacuum lines are good. Has GREAT vacuum. Boost to the approx. psi ad keeps it there. My guess is an ECT sensor being out of range or possibly a mixture of the MAF, TPS, an IAC. I haven't done much if anything to it lately except drive it. It drives great and gets great gas mileage still(27hwy). And it's just been to cold to be working outside on it. My ford truck had the same problem, and then got to where it wouldn't even idle all thanks to the ECT sensor reading that it was way colder than the actual air temp. Making a rich condition. I'm thinking this would do the same thing.
If it were the ECT that would also explain the hanging idle and the surging. ECT is going to ALSO control the TPS to some degree. Reading that it needs more air and fuel it will create the rich mixture and open the throttle, the o2 sensors are going to see this and realize that it is running rich and stop fuel flow, thus creating your "surging" idle.


it could also be the MAF sensor getting false readings(more air than what is actually being brought it, or a "surge" of air). I found this problem out with the newer mustangs that people put cone air filters(i do not have on tho) on with out a air box. When the cooling fan would kick on it would make the MAF read more air volume than there actually was, giving it more gas, makeing the car surge and coming up in the live datastream as a rich mixture setting off the check engine light. Being that our cars don't have quite the ECM the newer mustangs have, I'm gonna start with the ECT sensor.

Also my temp gauge is erratic, furthering my suspension of this sensor.

If someone thinks other wise, please let me hear your input. Thanks.
 
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I suspect the ECT has something to do with the issues I've had, when the car is at or above operating temp (hot Vegas days) it will cut out near to 4,000 rpm as if it were governed while under wide open throttle. If I would unplug the ECT it would run right up the rpm range as normal, however, the idle was non existent and erratic. I replaced the ECT brand new with no change, I replaced the thermostat with both a 180, then a 160 which only heat soaked the radiator, then back to the 192. I read here that new IAC valves (aftermarket) caused more problems than they were worth, so I replaced mine with two different valves from our local pick a part. Same result, no change. I replaced the MAF with a used one as well which also nettted little to no change. Really open to any suggestion cause its about ready to go down the road and it is truly a beautiful car. On a side note, the fuel gauge has never worked above the 1/4 mark even after a new pump/sender/tank, and gauge (well the gauge was used) I suspect this car has a hidden wiring issue that is causing these problems. There are just soo many to check...
 
So, today I changed out the temp sensor and replace the thermostat since I was there any way and it needed replaced. Took almost 60 miles for me to get descent warm air.
I replaced it, and great hot heat now, and temp gauge works. I found that the SC belt had rubbed completely thru 1 wire of the crank sensor wiring harness an was on its way to go thru the other 2 that was in the loom. I spliced the wires back and rerouted the harness so it wouldn't happen again!

After this the car started kicking down the idle to about 1000 and didn't rev up to the 15-1700rpm range. I can push in the clutch and the rpm drops as it should but still not to the 800rpm range. If your at a stop light for a bit it still kinda revs up an down. 1000 rpm to bout 1300, and then back down and back up, and does this for about 20 or so seconds and finally just summers down and stays at the 1000rpm range. And slowly ideals to about 900.

After repairing the wiring my tach is even more intermittent working and not working.

I still don't know what is causing the "surging".

Any other input on the subject would be greatly appreciated. I'm thinkin maybe the iac. Does anyone have the values for checking it?(ohm resistance or volts?"

Thanks
 
A jumpy tach sound a lot like a bad cam sensor, or at least one that is on its way out. Good luck on the specs, i've seen them posted here but cannot remember who put them up.
 
I thought the tac was ran off the crank sensor?
It actually taps off the DIS module. But the cam sensor typically makes this happen. The DIS itself can also cause the problem.

With the idle surge, Id double check the IC tubes and for any vac leaks. Suspect areas are anything that was touched during a recent repair. IC tubes and the SC top, and especially where the return IC tube attaches to the intake. If you did work around the dash, theres vac lines for the AC, the boost guage, and the cruise control.

After that, theres the IAC itself. Not a bad idea to have a spare. Also, if anyone monkeyed with the throttle stop screw, slap them. The throttle plate should be closed lightly with no throttle. The EEC controls the idle through the IAC. Its not uncommon for people to mess with it when trying to fix low idle.
 
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Well I've checked and checked for leaks and have had it smoked. Everytime shows up nothing. I'm fairly confident in the person that did the work as well. I'm a ford tec and I worked with the older guy that did the work, and he's pretty good around a sc. But I quite working there so I haven't had him look for any other problems as its $95 labor hour.

I notice right after I bought it that the throttle would stick if you let it slap back, like the blade would almost wedge in the bore, I noticed that the throttle stop screw was adjusted so far out that the screw didn't even touch the throttle stop plate. When I replaced the coupler in the supercharger I tightened the screw to we're it made contact with the throttle and twisted the screw about 1/2-3/4 turn further so I could see the blade barley open.
It hasn't affected the idle by keeping it higher. And since I've replaced the temp sensor my idle has been down more, and it seems the warmer it gets out the quicker it seems to idle down, but still not right. And the way it idels an surges varies from day to do.

I haven't had the time take the iac off an block it off and see what that shows.

I sealed the IC top tube to the intercooler when I replaced the coupler

The car has had the head gaskets replaced, supposedly they also milled the heads. I have the paper work showing the work done.

after driving The car in town whenever you push the clutch in it jumps to 2k and stays there for almost the entire time when sitting at a stop light.

It's just annoying having it idle so high just sitting there.
 
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