Idle problem (from Hell?)

[The-Q]

Greetings,
I have a terrible idle prob. on my '93 Ex. XLT. 4.0, auto, 4WD, 90,000 on motor. Suddenly, the idle is rough and choppy. I pulled codes (with a test light) and got 157, 158. I reset codes after cleaning the MAS several times, once with brake cleaner. Once or twice with carb cleaner. I still get bad idle and same codes. I checked voltage to MAS-14.0 volts, and the filament .750 volts. All within repair manual specs.
This idle problem started out of the BLUE! nothing was changed, adjusted, or fiddled with. I believe the 157 and 158 codes deal with MAS problems. ANY help is greatly appreciated. Thank You,

GQ

 

[ExplorerDMB]

157 - Mass air flow (MAF) sensor circuit below minimum voltage
158 - Mass air flow (MAF) sensor circuit above maximum voltage

I personally have never seen that before (having too low and too high of voltage). I would look into replacing the sensor.

-Drew

 

[Diff Whack Daddy]

Yeah, it sounds like cleaning it is no longer useful. I would deffinately look at swaping it.

 

[badgett]

I had a 94 that was showing those codes. I don't know why but it ended up being the throttle position sensor. It must have been throwing off the MAF. I put a brand new MAF on the truck. No help. When I got around to replacing the TPS, problem solved !

 

[MrShorty]

What type of codes are they (KOEO, CM, KOER)? If that doesn't mean anything, read my "notes on pulling EEC-IV codes" in the EEC-IV forum. It helps us get on the correct branch of the diagnostic tree if we know what type of code each is. Also note any pass codes. SOP is to resolve KOEO codes, then any KOER codes, and finally the CM codes.

Remember that codes point to problems in circuits, of which the sensor is only one part. There are also possible causes outside of the EEC-IV system (such as incorrect fuel pressure). One of the first tests fuel control codes like to see is a fuel pressure test (see Glacier's fuel pressure mini-diary in this forum).

MAF is one of the key sensors in controlling air:fuel ratio. Sometimes (as noted by badgett), the computer will flag the MAF when the fault lies in one of the other key A:F sensors (TPS, O2 come quickly to mind).

Again, the next best step will depend on what type of codes they are.

 

[ExplorerDMB]

157 - KOER
158 - KOER KOEO


-Drew

 

[The-Q]

Hi Again,
WoW!, lots of good responses, thanks Folks. I noted MrShorty's reply and will add to my original post. The error codes I pulled from my Ex. of 157, 158, were done KOEO. Also, I noticed that when the engine is idling rough and displaying the CEL, the engine seems to be running very rich, i.e. black exhaust smoke, fuel smell, and when I pulled the 6 spark plugs, the pass. side bank were very sooted and black! While the drivers side bank were normal color. Any further ideas?
Once again, Thank you to anyone who has, or may have occaision to leave a helpfull reply concerning this problem.

Regards,
GQ

 

[btimby]

yeah pull out and clean your idle air control valve too

 

[MrShorty]

Two of the three types of codes are output during the KOEO test: KOEO (hard fault codes) and CM (memory) codes. You pulled those codes from the KOEO test so that means:

157, which my list says can't be a KOEO code (and as noted by ExplorerDMB), would have to be a CM code.
158, which can be either a KOEO or a CM code, is still uncertain. If it was a KOEO code, then the first thing to check would be the wiring to/from the MAF. If it passed the KOEO test (KOEO 111), then the next step would be to get the KOER codes.

Interesting that it seems to only effect one side. I know some '93's had one O2 sensor, and others had 2. Do you know if you have 1 or 2 O2 sensors?

 

[The-Q]

MrShorty,
Thanks for the replies and info. My Ex. has two O2 sensors.

Regards,
GQ

 

[stang99x]

Get a hammer and tap on the IAC valve and see if it clears up. This is very typical of the new mod motors found in the F series truck and Expedition/Navigator. Chances are, the IAC isn't adjusting properly, and the rest of the system is trying to compensate, which is where you're codes are coming from.

I'd bet the farm its the IAC valve

 

[The-Q]

OK Folks,
The demon has been excorcised from my EX.
The crappy, fuel drenched, stumbling, rough idle, and the error codes of 157 and 158 are NO MORE. I replaced the MAF, and that was the fix. Thanks to all who took the time and effort to post a reply, it really is appreciated.
Time to do doughnuts!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Thanks,

GQ

 

[MrShorty]

Out of curiosity, was this a "guess and check, hope replacing the MAF fixes this" kind of thing? Or did you do something so you knew that the MAF was bad? I only ask because diagnosis can be 90% of a repair. Knowing how you determined that the MAF was bad (if you did) may be useful for future efforts at a similar problem.

 

[The-Q]

Replaced MAF sensor.

MrShorty,
To answer your question, I had a good idea of what the problem was because of the symptoms. I knew it had to be some type of electrical\sensor problem because of the rich-running and erratic idle properties. It seemed pretty clear that something was telling the engine to deliver too much fuel to the mix, and it would come and go as corraborated with the CEL. Also, the feedback I received from this site gave me a good idea of where to look for the prob. Once again thanks Mr. S., and all others who took the time to reply to my dilema.
P.S. a couple of days after the fix, I took a 180 mile highway trip and got around 14.5 mpg!!!!! a freekin' record for my Ex's ga-thirsty engine. normally around town I would get 7 or 8 mpg, and hi-way of 11 0r 12 mpg. Perhaps I had a strong tail-wind on my long journey, who knows????????

Thanx.

GQ