Idle problems

[mkostinec]

91 SHO 5 speed
110,000 miles
Ran fine until lately.

I have an idle problem. Starts fine. Idle OK for 15 seconds, then drops to 700 then upto 1200 then back to 700 until it final dies.

This idle issue was the problem with this car before I did any maintenance. It was the reason for the maintenance - I thought.

The first thing I did was do the top end 60K (first time ever @ 110,000). After doing the top and changing the O2 sensors – it had a idle problem – 3000+. Changed out TPS (Trottle position sensor)– problem went away for a day – then back.

Decided to do the 60K side job. Every thing looked good – except crank seal leaking a little. Change out timing belt, timing belt tensioner, front seal, CPS (crank position sensor). Put the O-ring on the water pump wrong – so coolant leaking (would that have effected CPS?). Now I have the side 60K job down to under 4 hours. –

Car still will not idle. Read some issues with the IAB – So I took off the IAB and cleaned – same problem. Next I replace the IAB – same problem.

I found out that if I made a hole in the vacuum line (Canister Purge) that goes to the top of the Trottle body the engine would smooth out it’s idle – Of course - the bigger the whole the higher the idle. The car will idle at a constant RPM.

Other information – changed out ACT (Air intake Sensor), and ECP (Engine Coolant sensor) – no change to way the engine idles.

The cars gets about 18 miles to gallon at 70 mph.

No other performance issue though the range – only idle issues.

For some time now the RPM gauge bounces around – some times it is correct – other times it seems to be off by 180% (should read 1100 – reads out 2000). Now lately, the RPM gauge will not seem to go below 2000.

I have messed with the screw on the throttle body that “I thought that my adjust the idle”.

I do have a small exhaust leak – most likely lost a manifold to Y-pipe stud – it has happen before.

It has the original fuel pump.

I have not check fuel pressure yet.

I have cleaned MFE Sensor.

I have spark at every plug.



Codes
KOEO – none and/or 11
KOER Codes are 13 (Cannot control RPM during self-test low RPM check. Suspect idle bypass valve problems) and 25 (Knock sensor (KS) not sensed during dynamic response test).

The error code 25 has come and gone.
The CE light has been coming on lately. Then when you push in the clutch and let the car idle down – the (CEL) check engine light will go off – so not sure what that is all about – haven’t see the problem in the last 700 miles.


Is the 25 code (can not sense Knock sensor) a issue?

Update!!!!
I rechecked vacuum hoses and clamps - now idles at 900 - but I don't expect this to last long.

The car also dies when coming to a stop. Speed Sensor? Where is this?

 

[todras]

I'd try a different MAF.

 

[mkostinec]

I quess it wouldn't hurt - I tried replacing about every other part. Where is the TACH getting it's reading from? Cam Sensor? How about replacing the Cam Sensor?

 

[F-22 Raptor SHO]

You are doing work to the car that is not related to ide...the 60k itself will not change the idle unless it was caused by a leak in one of the intake gaskets. The valve lash, cps, timing belt, waterpump, and such do not affect the idle.

Did you clean the intake and replace the upper gaskets?


the IAC (idle air control) valve located at the top of the motor near the TB might need a good cleaning out or could be bad entirely.

Also the Throttle position sensor could be bad as well.

Both of these devices are directly linked to how the car idles. I would attack those items.

DO NOT mess with that screw on the TB, it isnt meant to be screwed with which begs the question why is it even there......its there not to be touched.

 

[mkostinec]

One problem solved. Changing out the MAF Sensor did make some difference. I had put on the old IAC because I was not sure the new one was working correctly. After I put the new IAC back on and reset the idle - the idle is fine - for now. I will give it a few days.

But when I am put the car into neutral when coming to a stop - the car will die MOST times - not always. I suspect the Speed sensor will need to changed next.

I did clean out the intake and change the top gasket - infact I took the intake apart and changed out all the gaskets - except the trottle body gasket. I now have a throttle body gasket and may take off the throttle body and scub everything down inside.

I did change out the TPS.

 

[mkostinec]

One other thing.

The only code I am getting now is 25 - (Knock sensor (KS) not sensed during dynamic response test).

Is this a problem?

 

[perlitaj]

Did u ever fix this, mines doing the same thing. Surging until it dies.

 

[cetroutt]

when i did my top 60K i forgot to reconnect the MAF and when i started it up it idled like you are describing. i shut it off and connected my MAF and started back up and it has ran fine since. i would look into your MAF.

 

[perlitaj]

Mkostinec, again where you at with this. Mine problem is exacxtly the same as yours. I replaced the MAF and a little better but not a rock steady idle like it was before. I suspect it's a sensor but don't know and don't want to replace them all.

 

[frosho]

mkostinec hasn't been online in over 7 months. Just make a new thread for your problem.