Idle issue, tested everything. wtf..

[281pony]

i had my car dyno tuned via sct 4-bank chip. it has always idled good, warm start, cold start, whatever. out of nowhere it started to develop a slight rpm drop and faint surge when pushing in the clutch and rolling.

now it has gone full blown nightmare, and i have tested everything to no avail. here is whats going on..

cold start; surges badly and will 100% of the time die. i can nurse the rpm's down slowly with my foot. eventually i can gain control and it idles.

hot start; same as above.

if i start the car after it dies in neutral, sometimes it will idle perfect, more often it will continue surging like a bitch.

rolling it is about 2/10 times a normal idle, about 8/10 times it surges bad and dies. when approaching a stop at slower speeds, it frequently will just die as if i cut the switch. it also does this equally as often when rolling at any speed, push in clutch pedal and it is done.

it has all aspects of surging idle, hot, cold, moving, stopped. sometimes it even stumbles and starts surging from a neutral idle sitting at a light.

been over the jricher test list, it all checks out good. i have vacuum, wideband, fp gauges, everything is registering the same. went over all hoses, checked with multimeters. no codes. pulled my chip, same thing. reset battery, same thing.

any idea's? thoughts? the big problem here, is my dyno tuner is no more. so i can't go get him to check it out now..

 

[LarsD]

Do you run an oiled filter? I've been having trouble with my MAF getting dirty and causing all kinds of funky idle problems that aren't consistent. Every time it starts to do this too me, I clean the MAF and it clears up. I've been looking around at retrofitting an airbox back onto the car so I can run a panel paper filter again.

 

[jrichker]

Do the "Surging Idle Checklist set mechanical base idle proceedure and see if the idle will stabilize for the test. If it doesn't stabilize, you have mechanical problems. That means vacuum leaks, faulty injectors, weak cylinders or bad valves/valve springs.

Idle does stablize when you do the set mechanical base idle proceedure. That means you have electronic sensor or actuator problems.

Disconnect the IAC/IAB: does it still surge?
Yes - reconnect the IAC/IAB and check the timing advance with a timing light. Remember to remove the SPOUT when you check the timing. If the engine stops surging when you remove the SPOUT, your timing is definitely off.
No - clean or replace the IAC/IAB.

Check the TPS sensor - see http://www.stangnet.com/mustang-forums/825424-adjusting-your-tps-0-98v-not-necessary.html for help.

Check grounds:
2.) The secondary power ground is between the back of the intake manifold and the driver's side firewall. It is often missing or loose. It supplies ground for the alternator, A/C compressor clutch and other electrical accessories such as the gauges.

Any car that has a 3G or high output current alternator needs a 4 gauge ground wire running from the block to the chassis ground where the battery pigtail ground connects. The 3G has a 130 amp capacity, so you wire the power side with 4 gauge wire. It stands to reason that the ground side handles just a much current, so it needs to be 4 gauge too.

The picture shows the common ground point for the battery , computer, & extra 3G alternator ground wire as described above in paragraph 2. A screwdriver points to the bolt that is the common ground point.

The battery common ground is a 10 gauge pigtail with the computer ground attached to it.
Picture courtesy timewarped1972

Correct negative battery ground cable.

3.) The computer has its own dedicated power ground that comes off the ground pigtail on the battery ground wire. Due to its proximity to the battery, it may become corroded by acid fumes from the battery.
In 86-90 model cars, it is a black cylinder about 2 1/2" long by 1" diameter with a black/lt green wire.
In 91-95 model cars it is a black cylinder about 2 1/2" long by 1" diameter with a black/white wire.
You'll find it up next to the starter solenoid where the wire goes into the wiring harness.


4.) All the sensors have a common separate ground. This includes the TPS, ACT, EGE, BAP, & VSS sensors.

5.) The O2 sensor heaters have their own ground (HEGO ground) coming from the computer. This is different and separate from the O2 sensor ground. It is an orange wire with a ring terminal on it. It is located in the fuel injector wiring harness and comes out under the throttle body. It gets connected to a manifold or bolt on back of the cylinder head.

 

[281pony]

i cant say for sure wtf helps or doesn't help this car. i drove it after work today, it drove great for 20 minutes. i turned into my bank and pushed in the clutch and it just died.

then it started and instantly idled perfect. i slowly moved through the parking lot and then it died when i pushed in the clutch again to approach the atm. then it wouldn't idle for chit.

it will be fine, then screwed. it is not consistant, i have been over everything. i even checked torque on my intake, vss, unplugged stuff.

im so pissed because i had a really similar idle issue and my dyno tuner took care of it no problem. now this area has a dyno tuner crisis and i'm just f'd with this stuff apparently.

 

[jrichker]

It sounds like an intermittent bad electrical connection. Start jiggling wires and see if anything changes.