Persistant Code 12

[PushnFords]

A friend of my wife's asked if I would do some preventative maint work on her '88 Cougar since I have my CV and it is similar. Initial plan was to change the coolant hoses, water pump, and thermostat for preventative maintenance. I also replaced the PCV filter and valve, and replaced all of the rubber lines under the plenum. I also planned on replacing the valve cover, lower intake, and P/S hoses due to leaks. Everything was going decent until the top right water pump bolt broke off. I finally got it out using heat and welding a nut on it...then eventually drilled it out. Since I had the timing cover off I replaced the timing set...then was worried about getting too much heat in the block right next to the head gasket so I changed the right head gasket and fixed a leak at the exhaust manifold. I had the head checked for cracks/warping, cleaned it, then reassembled with new valve stem seals. I got everything back together and was getting a memory code for the EGR as well as KOER code 12 and codes for the smog pump system...plus it would barely idle with the A/C on and kept dying. All of my problems seemed vaccum related and I hadn't liked how the lower intake gasket set down so I replaced the lower gasket with a different brand. That eliminated all of my codes except the 12. I've been working on the car for two weeks as time allows since I got it back together and the owner really needs the car back.

I've been trying to read up on the KOER code 12 and everything points to a vacuum leak or bad IAC valve. I just redid the intake gaskets and am pretty confident I don't have a leak there. I've also swapped in a used IAC valve that was on a HO plenum I bought at a swap meet. I found a couple of people mentioning that the throttle plate screw being tampered with can cause problems...and if idle is too low you can turn it in slightly as long as you don't throw the TPS sensor out of range. I've been using an F150 Haynes manual for specs and they said .50-1.0V for the TPS. I tested it and got .875 so I turned the idle screw in 1/2 turn and then adjusted the TPS to .994V. So here's where I'm at:

TPS voltage @ idle = .994V (in spec)
IAC resistence = 10.4 Ohms (in spec)
IAC input voltage = 11.7V (spec in book says 10.5V)
Idle rpm = 580-620 depending on idle quality (in spec)
Engine vaccum @ idle = steady 18 inches

While I know that sensors could have gone bad while laying in the garage during my time working on the engine...it doesn't make a lot of sense. The car ran fine before I tore it apart. Now I'm wondering if some of my welding messed up the computer and that's why I'm getting the higher IAC valve input voltage? Would that cause the code? I'm assuming I could probably swap the computer from my CV in temporarily?

[1990LTD]

If you welded without disconnecting the battery...it could have messed it up.


The Cougar has 351 firing order and 19lb injectors. The CV computer = 302 firing order and 14lb injectors. Don't think it will work.


I could be wrong about the Cougar being HO but I think lincolmania has a HO in his 92 from a Cougar..

[86VickyLX]

88 Cougar is a Lopo. Set the TPS to .9V at closed throttle exactly, set timing to base 10 degrees btdc, disconnect battery and reconnect. Try again.

[gadget73]

the TPS OK range is something like 0.7-1.2 volts. 0.994 is just fine.

12 is high idle. I'd probably try swapping the IAC again, or at least cleaning it. It sounds like its still sticky.

[PushnFords]

Some info I left out of the first post. Tonight after checking the adjustments I capped off all of the vacuum lines one by one, ran a KOER test, then reconnected that vacuum line and moved to the next. By doing that I isolated the smog system, the vacuum tee that feeds the booster, and the plastic line going to the EGR solenoids. I got various codes relating to the parts I had disconnected...buy also got the 12 EVERY time.

If you welded without disconnecting the battery...it could have messed it up.

The Cougar has 351 firing order and 19lb injectors. The CV computer = 302 firing order and 14lb injectors. Don't think it will work.

The battery was disconnected for all welding. The car is an XR7 but doesn't say HO anywhere on it and has the lopo firing order...I replaced the plug wires.

88 Cougar is a Lopo. Set the TPS to .9V at closed throttle exactly, set timing to base 10 degrees btdc, disconnect battery and reconnect. Try again.

When I first checked the TPS voltage I was at .875V or so and had the exact same problem as I do now. Changing the throttle plate screw position and TPS adjustment gave me a slightly higher idle (still within spec) but the engine runs the same. Timing is at 10 BTDC.

the TPS OK range is something like 0.7-1.2 volts. 0.994 is just fine.

12 is high idle. I'd probably try swapping the IAC again, or at least cleaning it. It sounds like its still sticky.

The Haynes manual said .5-1.0 volt and I saw a little higher mentioned online. Funny thing is most places talked about idle quality problems even though it is a "high" idle code. I'll try the IAC off my CV tomorrow.

Any thoughts on the input voltage? If voltage opens the solenoid then would a slightly higher voltage hold it open a tad and cause a "vacuum leak"? I'll probably check the voltage on my CV tomorrow as well. It has a vacuum leak under the plenum at the moment and last I checked it had a couple of codes so not the best thing to base tests against.
IAC input voltage = 11.7V (spec in book says 10.5V)

[86VickyLX]

Leave the throttle screw alone. Adjust the TPS by moving it on the throttle body by loosening the two hold down screws. As for input voltage the way I figure it, it would be more because the computer is trying to slow down the idle speed. The computer controls the IAC on the ground side, there's always a 12v source applied to it, since the IAC receives power from the EEC relay. The closer to 12v the ground wire (tan I think) is, the least amount of time/ amount the IAC is open. It could be a vacuum leak, but there are no other codes that support that (lean codes etc). Are there any driveability concerns besides this 12 code?

[gadget73]

if you unplug the IAC, how much does the idle drop? It should drop to 500 rpm or so, which is too low. The IAC will open up some to control that. If the idle doesn't drop below spec with the IAC unplugged, then it can't control idle speed properly.

[PushnFords]

Leave the throttle screw alone. Adjust the TPS by moving it on the throttle body by loosening the two hold down screws. As for input voltage the way I figure it, it would be more because the computer is trying to slow down the idle speed. The computer controls the IAC on the ground side, there's always a 12v source applied to it, since the IAC receives power from the EEC relay. The closer to 12v the ground wire (tan I think) is, the least amount of time/ amount the IAC is open. It could be a vacuum leak, but there are no other codes that support that (lean codes etc). Are there any driveability concerns besides this 12 code?

I'm keeping track of where the throttle screw started and where I've moved it to so I can reset if need be. I turned it in 1/2 turn and then adjusted the TPS like you said to get the .994V.

I measured the input voltage with the engine off, key on per the manual...so the computer shouldn't be adjusting it to compensate for idle. If I catch enough of a break between thunderstorms I'll do some more checks.

The car idles rough...sometimes more than others. Sometimes won't start on the first try and sometimes won't idle well. Helps if you give it gas after it fires but sometimes it'll die immediately. Sometimes will idle for quite a while and then die. Sometimes dies when you slow down to stop. Running the A/C makes things worse. Sometimes it'll die at idle with the A/C on and won't restart unless you turn off the A/C. Other times it seems to run pretty good.

if you unplug the IAC, how much does the idle drop?

It dies immediately like the key was turned off and won't restart.

[gadget73]

ok, thats good then. often if the throttle screw has been adjusted, its turned so far in that the car just runs without the IAC even connected. As long as thats not the case, you're OK with the throttle stop screw.

[PushnFords]

I put the IAC from my CV on it tonight, disconnected the battery cable for a while, then drove it around 20 miles. Got back...still have the code 12. The car seems like it has a constant miss. Not very bad at speed...hardly noticable...but I think it is there. I did have it miss briefly between 30-35mph when I was in town driving on the way back. The other thing I've noticed is that it is a dog. On my CV if I gun it to get across an intersection it'll spin the tire for a ways. I stopped on a flat section of highway in the rain and floored it...BARELY spun at all.

I'm to the point of double checking everything I did. I was thinking about the timing chain tonight. Almost positive I double checked it and got it lined up correctly....but if I was a tooth off what would the symptoms be? It doesn't pop out of the intake or exhaust like I'd expect if the timing was off too much......

[86VickyLX]

I put the IAC from my CV on it tonight, disconnected the battery cable for a while, then drove it around 20 miles. Got back...still have the code 12. The car seems like it has a constant miss. Not very bad at speed...hardly noticable...but I think it is there. I did have it miss briefly between 30-35mph when I was in town driving on the way back. The other thing I've noticed is that it is a dog. On my CV if I gun it to get across an intersection it'll spin the tire for a ways. I stopped on a flat section of highway in the rain and floored it...BARELY spun at all.

I'm to the point of double checking everything I did. I was thinking about the timing chain tonight. Almost positive I double checked it and got it lined up correctly....but if I was a tooth off what would the symptoms be? It doesn't pop out of the intake or exhaust like I'd expect if the timing was off too much......

Also check the injectors, like the orings, I've seen it where they suck air past the injectors into the cylinders. It does weird funky stuff.

[PushnFords]

Also check the injectors, like the orings, I've seen it where they suck air past the injectors into the cylinders. It does weird funky stuff.

I cleaned the intake up really well when I had it apart. Soaked it in a solvent tank for a couple of days and then power washed it. Sprayed the gunk off the injectors with carb cleaner...sprayed from the side so it wouldn't force gunk up the tips...and reinstalled everything with new lower o-rings. I reused the upper o-rings but those would probably leak fuel vs. suck in air.

[86VickyLX]

I cleaned the intake up really well when I had it apart. Soaked it in a solvent tank for a couple of days and then power washed it. Sprayed the gunk off the injectors with carb cleaner...sprayed from the side so it wouldn't force gunk up the tips...and reinstalled everything with new lower o-rings. I reused the upper o-rings but those would probably leak fuel vs. suck in air.

Did you lube the o-rings?

I watched someone do a new set of injectors in a certain '92 Grand Marquis with a 5.0, with brandy new injectors, and I watched that certain 5.0 suck air past the o rings. Even after he did everything as it was supposed to be done. Grab some WD-40 and spray it around the base of the injector, if it sucks the stuff into the cylinder, you have problems there.

[PushnFords]

Did you lube the o-rings?

Yes I did but I'll check them tonight. I've never installed a timing set a tooth off but that thought has been occurring to me as well. IDK...running out of stuff to check. And...I'd rather tear it back down and find the timing set off myself then have someone else find it.

[PushnFords]

No leaks found around the injectors...and the timing chain was indexed correctly. Hope to have it back together tomorrow. It is damn hot out.