Fluxing idle

[silver93sho]

Newer issue with my 93 mtx. Stopped at a light the rpms will be stable then start to jump around like up to 1500 and down enough that the oil pressure light will come on and she will stall if i don't tap the gas. I have pulled codes and it seems both O2 sensors are bad. I intend to replace them soon but those codes where stored so im not sure how long its been that way. I can toss in another cam sensor but wondering if anyone else has had this issue before?? Another part of it is if it does stall it doesnt like to start again, it will just crank away. Ideas??

 

[rubydist]

surging idle is nearly always due to a sticking iac. I have never seen a cam sensor cause it.

you can reset the codes and see if those o2 codes return.

 

[silver93sho]

Good point on the iac...I'll take it off this weekend and clean it and reset the codes. I haven't checked/cleaned it (iac) in years.

 

[silver93sho]

So I pulled the iac and it was nice and clean, reset the system, did idle air reset and drove it, codes immediatly reset with all the 170's for the O2 sensors and a 411 (bad idle) code. still having the same issue with the fluxing idle. crazy thing is parked here at home it will run just fine for as long as i let it go??!! but driving it will keep fluxing non stop. i noticed tonight that the set screw on the throttle body is gone...it must have worked out at some point. not sure where to go from here!

 

[93markVIII]

missing set screw a vacuum leak?
or other possible vac leaks?

 

[1320n2oSHO]

My 91 will SOMETIMES have a rolling or fluxing idle after driving it for a while when I turn it off for say 15-20 mins and starting it back up. I haven't pulled codes or anything cause it only does it on occasion but ill go through it tomorrow and post it here if I find anything that might help you. Ohh also my heater and AC only blow on defroster so I'm suspicious of a vacuum leak on mine, yours could be related to your missing set screw possibly causing a vacuum leak

 

[rubydist]

1. what are the o2 codes?
2. you should change the tb to one that has the setscrew in it - its there for a reason.
3. just because the iac looks "clean" does not mean it will work right - I have had a brand new out of the box iac be sticky and surge like crazy.
4. I also suspect that part of the problem is a vacuum leak, but you need to fix the throttle body first. PM or text me and I can give you one from my collection.

 

[silver93sho]

93MarkVIII/1320n2oSHO- the set screw on the throttle body is set by the factory to keep the throttle body valve from closing too much, ive never touched it and it couldn't cause a vacuum leak, theres no lines and its attached to the outside of the TB and mates up to the spring loaded assy from the throttle cables.
rubydist- yes i know i need that screw, just don't have one now or know the pitch of the thread to put one in. o2 codes: 172,173,176,177 so both o2's not switching. i never thought of a vacuum leak and that makes me think that's a good culprit. I will be checking on that this weekend. Also I did send you a PM a few days ago with my number in it but Richard sent me your number so I will text you about the set screw, i know its the holidays so if not til after thats fine but ill drop you a txt. And i do agree about the iac looking ok but not working properly...i do have a 411 (bad idle) code too.

 

[rubydist]

ok, you should first reset the codes. The easiest way to do that is to pull off the jumper wire while the codes are still flashing. Then drive the car for a couple of days and check the codes again.

The reason for this exercise is that I have never seen a legit set of BOTH lean and rich codes on both o2 sensors at the same time (which is what you have reported). I think you have some ancient codes in there which may be misleading you as to the real issues.

Let us know what you find.

 

[silver93sho]

i reset the system the other weekend and have driven the car a few times. today i checked vacuum hoses and didnt see anything bad, also cruise control works, if that helps. went for a 10 mile drive today around here and idle was fine except for 1 stop light where it dropped and stalled, next light it was fine. pulled codes just now and got these: 121 in first set of codes then these in second set: 157, 173, 177, 542,556,557. i think the 500 ones are because of stalls?? 121 is TPS out of range, 157 is MAF and 170s O2 sensor.

I know i still need that set screw but im really thinking now its a sticky iac because the day i drove it to work it wanted to stall almost everytime i came to a stop then today it ran mostly great.

 

[tery]

fluxing idle possibility.

Has anyone heard of this problem being caused by a bad coolant temp sensor. They guy who sold me my SHO said he thought it was that when mine is doing the stalling problem.. I have noticed that the temp gauge is very slow to rise and then when the idle stuff happens, there is often movement in the needle of the temp gauge on the instrument panel that just doesn't look right cause its quick flicks and stuff, Then sometimes, when it has been running a longer time and I have restarted several times, and the gauge reads full normal operating temp, the stalling problem seems to go away. Mine does that same thing..surges before very low rpm to stall cycle....not every time but mostly that seems to be the pattern, I've only had it a while and am trying to figure it out. I'm taking it i Monday for brakes and I'll find out what the codes say

 

[rubydist]

ok, now we are making some progress. The 121 (tps out of range) and 157 (mafs below minimum voltage) are related, and are an important part of the problem. Those 2 sensors are both on the same power circuit from the pcm, and when there is a problem with multiple sensors on that circuit it is a power/ground issue, not a sensor issue. Most likely that circuit has a bad ground, or one of the connectors is corroded up and causing a big voltage drop across it, making the pcm read the sensors wrong. Look for bad ground and bad connectors. Once that is fixed, there is a good chance that the rich codes will go away on their own, and the surging idle may be gone as well.

tery, the sensor that drives the dash temperature gauge does only that - it has no effect on how the car runs. There is another temp sensor (with 2 terminals) that is connected to the pcm - that is how the pcm 'knows' the coolant temperature. Wild swings in the dash temp gauge are typically due to a corroded connection of the wire on the temp sensor on the engine, or a bad ground of the engine. Note that the bad engine ground can cause all kinds of issues, including the engine not running at all.

 

[tery]

thank you Ruby

Wow! what a great forum, Yeah, ground issues...I bought it for 1g cause the engine and tranny sounds and runs great, but when I took it in today to get the brakes and things checked, it turns out that the underbody is so rusty that they won't even work on it. It needs a tie rod, lower Lf ball joint and bearing the right cradle mount is gone and someone ghetto fixed it with a welded L shaped piece. The car pulls right intermittently and they told me that it was because the body and the frame are so rusted it is sort of shifting on itself. I was thinking I'd spend the summer putting this thing is good order, but now I'm not so sure that is a reasonable thing to do..
I'm going Friday to see a welder to see if he thinks he can save the unibody. If not I may just have to part it out cause no one wants to work on it..safety issues I guess, and my back won't put up with that kind of work on cars anymore. The exterior of the car is very good. The seller said he hit a deer so there is a bit of a crumpled hood, but it closes
Any thoughts Ruby??
Thanks again for the quick reply

 

[rubydist]

living in the west for the past nearly 20 years has spoiled me - I refuse to have or work on stuff that is rusty. There are plenty of decent examples of Taurii around. Save the good stuff and look for another SHO that some idiot wrecked the motor or tranny on and buy that for a song and put in your good stuff.

 

[tery]

Thank you Rubydist. I will be looking, but until then am going to go ahead and meet with a welder on Friday just to see if it is salvageable. I can see sense to both sides, but I do get a kick out of bringing something back to rights.During the summer I would be free to go and look for a who that didn't have to go through MN salt.
I'll keep posting with updates. I got a picture up if you want to see it.
thanks again for the help
Terry
http://s935.photobucket.com/user/tgresser/library/