missing at idle and stumbling down low

[SHOrus]

My SHO will sit and miss at idle. Not horribly to the point of dying, but not good, obviously. The idle part gets noticeably better when it warms up.

The other problem is if I'm driving along at a low RPM and mash it, it misses again and has not nearly enough power. At high RPMs, it seems like it 'clears up'. This seems to have never gone away, warm or cold. Any ideas?

 

[FREAK_SHO]

Codes? When were the plugs and wires changed? Bad IAC? Checked for vac leaks? Pull plug wires and check for oil in the plug wells.

 

[1995mtxsho]

Coolant Leak/Air in system... or a fouling plug due to oil in the plug wells... or both.

 

[SHOrus]

Plugs and wires were changed a matter of days ago. What exactly is the IAC?

 

[Lightning]

Idle Air Control

The purpose of the IAC motor is essentially to provide a controllable vacuum leak. The ECU can command the IAC motor to open and allow more air to enter the engine, or it can command it to close and allow less air in. More air will mean more engine speed and vice versa, so an IAC motor can be used to control engine speed. As seen in the graph below titled "Idle Speed vs. Coolant Temperature", a desired engine idle speed can be programmed by the user, and the ECU will use the IAC motor to keep the engine idling at this speed. However, as the throttle opens further and engine speed goes well above the targeted idle speed, the ECU will tell the IAC motor to close all the way in an attempt to bring engine speed back to its targeted value.

Google is a beautiful thing...



available for ~50-60 bucks. Controls the idle in your SHO. Search the forum, lots of information about testing them...

 

[St Louis SHO]

Firing order correct? It is known to be wrong in some manuals.

 

[SHOrus]

Had it at a friends shop about an hour ago. Don't remember the exact codes (I think one was 50 and one was 172, don't remember the one other one), but it basically said something's up with cylinder 5 (front center cyl, correct?) and front and rear banks are running lean.

They told me the cyl 5 thing is probably an injector or plug wire issue and the lean condition is most likely (sounded like) an exhaust leak.

 

[St Louis SHO]

Did you check spark at the coil? I've had just 1 wire at the coil with no-spark.
Edit: A lean code is when the ECM is having to dump more fuel in 1 bank, so which bank was lean? Must have been bank 2, from the sound of #5 cyl related codes.

 

[SHOrus]

I have an extra coil pack that I believe to be good. Should I give that a try on there? I suppose it wouldn't hurt.

Also, it was throwing a lean code on both banks.

 

[St Louis SHO]

Check the spark first by lifting the wires (one by one) and starting it to check. Its sounding more like a vacuum leak now.....

 

[SHOrus]

Are there any particularly common places were vacuum leaks occur?

 

[SHOrus]

btw, checked plug wells and they're free of oil.

 

[FREAK_SHO]

172 HEGO sensor circuit indicates lean. O2 Sensor...Either bad sensor or you have a vac leak.

When you changed the plugs and wires, did you remove the intake? If so, check for vac leaks starting there.

MAF Clean? Get some CRC MAF cleaner and clean the MAF, this can cause issues as well.