Three Possibly Related Idle Problems

jonroe

Registered User
This has been bugging me for awhile but I'll try to be brief. For the past several months I have been suffering these three (possibly) related idle problems with my, otherwise perfectly running, 93 SC.

1) Car does not want to idle upon a cold start. Will idle for 10-20 seconds and then try to stall and I need to play with the throttle for a minute or two for it to run on its own.
2) When warm and under normal driving nearly EVERY time I come to a stop and put in the clutch the idle goes up to about 1700-1800 as I approach the stop. It stays up there until I'm stopped for 5 - 10 seconds then slowly drops back to normal.
3) When warm and under normal driving after it sits at a long light, between 1 and 2 minutes, the idle will suddenly fall to about 500 from 850 and get rough. Again, I have to play with the throttle to get it smoothed out again.

These three things are driving me nuts. I can't find anything wrong. I've done all the usual diagnostics with no codes at all, can't find any vaccuum leaks, and recently replaced the IAC with a new Ford unit. There are NO driving problems whatsoever off idle.

Any more suggestions? Thanks.

Jon
 
believe it or not.. check the motor mounts. I had the same issue, and finally found the problem, busted motor mount. The engine was vibrating and hitting metal to metal, ( rubber gone ) and fooling the anti-knox sensor causing the rough idle.
-Keith
 
SWAG, clean MAF sensor wires with electrical contact cleaner, change O2 sensors, reset A/F memory by disconnecting battery for a while.
And search 'Cam sensor', 'Crank sensor', and ' Harmonic Balancer'.
 
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Iac

I had similar symptoms and corrected it by replacing the IAC Idle Air Control valve that is connected to the TB. Just another thing to check and my 2cents.
Dan
 
Check egr valve

My 89 is like that as I took it through inspection and failed emission for egr valve, mine doesn,t idle til it warms up also,!! Ju st something you can look into ya know!
Oh yeah, I changed the TPS and still did it,my 2 cents
 
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i had problem #2. every time the clutch went in rpms kicked up to 2200and held.

i went thru 2 IAC's. 1 GP sorensen and 1 ford. didnt work

bought a new TPS. didnt work

changed plugs and wires and re-sealed the IC tubes. that didnt work.

so i was convinced it was a vacuum leak. pulled the SC, inlet and TB off and where the return plenum bolts to the intake manifold.....2 of the 3 bolts that were run up about half way, letting all the extra air it wanted in.

i was also throwing codes 41 and 91 for running lean.

hope this helps.
 
Thanks for all the thoughts.....my comments:

I could check the right motor mount. I changed the left one a couple of years ago. I don't see any problem with oil filter or steering line clearance underneath.

I have cleaned the MAF, have disconnected the battery, no computer codes. Could it be a very dirty air filter? It's a MAC down in the fender and I haven't cleaned it in a long while. In the next week or so I plan to replace the MAC with the SCP air intake.

I have a new TPS and will install when I do the air intake. The IAC is brand new Ford. This car has no EGR.

Could still be a vaccuum leak as you say. I don't have any lean running symptoms and no codes but I should look at the bolts.

I'll let you know as I progress.

Thanks, again.

Jon
 
Folks,

I hate to dredge this up again but there is new information.

I have now replaced the MAC CAI with the SCP CAI under the hood including new cone air filter. When I replaced the CAI I replaced the TPS as well.

The 3 basic problems still exist, runs rough on cold start for a few minutes, races above idle when coming to a stop while putting in the clutch, and wants to die after sitting at a light for about a minute. In the last few days add the dreaded dropping tach needle. It happened to me once last week and twice today. I was cruising at 60 on the freeway and the tach needle dropped to 0 and immediately came back with no engine problem. Still no codes.

Any more help, please, for the these now 4 problems? I am very frustrated and I'm not sure I can rely on driving it any distance. Jon
 
I have pretty much the exact same problems exept for the racing idle when the clutch is pushed in when coming to a stop...otherwise the exact same problems :(
 
Sounds like a small vacuum leak...try spraying all the IC tube connections and vacuum hose connections with carb cleaner while the motor is running.

David
 
Its doing the same thing my 93 used to do. Im willing to bet its your DIS module! Check for cracks in it and that the wires are plugged in well. If you cant afford to buy one. See if you can borrow one for a second from someones car that runs good to test it. Also, how do you coil packs look?
 
You know...

I had a strangely similiar problem, it would idle fine for a while then sitting at a light then all of a sudden, the rpms would drop just a little and cause the steering to get hard.

I checked the IAC, etc...all were fine, etc.

Well, I figured it could be the PS Pump as it did get harder to turn the wheel when it did that.

So, I went under the hood, the top of the pump was lodged against the side of my car's fender [and I didn't notice without looking closely where the two tabs attach to the base of the pump], so I undid, rotated it, snapped it on tight, no more idle problem.

It's weird, I know, but it worked...
 
One reason i dont think mine is a vacuum leak is that once the car warms up its not nearly as bad. I also am going to do sprak plugs to see if thats it...just havent had a chance yet. If the plugs dont work them in doing a DIS module.
 
Had close to the same prob. No codes.. It ended up being the cam sensor.. It was intermittant..It never gave me any codes.. I rplcd it and have not had a problem since..


Tony63
 
Thanks for your further input.

I presume that the idle problems are probably separate from the tach needle drop and just a coincidence.

I will try the vaccuum leak test. I had a slight leak before at the lower IC connector (you could see oil residue), tightened that and have not seen the oil residue come back. So far I don't hear a vaccuum leak. You'd think you would hear it if it was causing the racing when I put in the clutch.

The DIS is fairly new but I could inspect it and replace the heat sink grease.

It sounds like what I see here and reading archives that the tach needle drop is most likely the cam sensor going south?

Jon
 
Mine done the same thing it would idle bad but when i warmed up it wasnt that bad but when i was driving and i would push the clutch in the idle would go up mine was a vac leak the pvc hook up on passenger side that goes to the supercharger had came off check that
 
Latest news from frustrated me........

Last week while cruising the freeway I saw the tach drop to zero for several seconds followed by a CEL followed by tach back to normal followed by CEL going out. This happened twice in a couple of minutes. Has not happened since.

I pulled codes today and got 212 and 214 in the stored codes while doing the KOEO. The 214 is CID lost which seems to be the Cam sensor. The 212 could be a secondary result of the 214 where the tach gets no signal from the DIS. So, my problem indicated here could be Cam sensor and/or DIS. Today, I also took off the DIS, cleaned the heat sink areas on it and the A/C carefully and re-installed with a carefully applied layer of fresh heat sink compound. I have not started it since.

With regard to the idle, the last two days are driving me nuts. Yesterday I drove it quite a bit and did not have much of the racing idle but did have the "wants to stumble and die" while sitting more than 30 seconds idling. Today, I had serious racing idle every damn time I came to a stop. Before, the racing idle was around 1600 rpm while today it was over 2000 rpm. Is there any way this bizarre idling problem (racing while coming to stop and trying to die at stoplights) can be related to the cam sensor and/or DIS? I will replace the cam sensor next when I get a chance.

Pretty soon I'm taking it into my trusted mechanic and if he can't fix the damn thing I might get rid of it. It is such a total pain in the ~~~ to drive around city streets yet runs perfectly on the highway. I'm at the end of my rope.

Jon
 
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