94 f150 w/302, 93 ignition

Codes:
KOEO-
337= EVP above maximum voltage
Continuous-
212= Loss of ignition diagnostic monitor signal to PCM or spark output circuit ground
337= ---
556= Fuel pump relay primary circuit failure
Engine running-
412= IAC cannot control low idle
411= IAC cannot control high idle
337= ---
311= Secondary air inoperative
83= EGRC circuit failure

I've taken off the EGR valve(intake tube had a large hole in it) and put a 4.7K ohm resistor in its place from power to signal and power to ground(as the position sensor measured). Then I put a 10k ohm resistor on the EVS to let the computer think it was a complete circuit. I also took off the air emission pump for the thermactor system(pump is severely messed up, tubes have cracks). The TAB and TAD also got a 10k resistor in their place.

The truck at times seems to lack alot of power. The throttle hangs when I let off.

As for code 337, I've almost got that solved.
I'm stumped on 212. The ICM and PIP sensor have been replaced. I've cleaned the surface between the distributor and intake manifold to ensure a good ground. The ICM is grounded well, too.
Code 556. I've replaced fuel pump relay, cleared codes, and still got this. The pumps sound like they work fine(in both tanks).
Code 412 and 411, resistance and voltage checks came out good. I also cleaned it out and that made little change in the idle problem. I'm replacing the IAC this afternoon.
Code 311 is caused by that all being disconected.
Code 83 is also being checked out.

++++ I need help with code 212 and 556 ++++ What should I do first?
Any help or suggestions with the other codes is appreciated as well

 

Well, I just got back from the weekend. Instead of replacing the IAC, I cleaned it out and put a bead of silicone around where the metal casing meets the cast part. That fixed the idle. It stays consistant now with no jumping around.

I still have the throttle hanging though. This has become a somewhat dangerous problem. I locked the front tires up the other day and barely avoided hitting someone. The throttle was stuck at 2,000rpm. So now everytime I need to stop I have to put the truck into neutral for a brief moment. Again, once I put it into neutral, the throttle drops back down.

I will pull my codes again later.

(I also mistyped something in the original post. Its supposed to be EVR not EVS. Why can't we edit post later on these forums?)

 

I'm guessing that the lack of EGR is causing the idle to hang. I noticed that on my truck when I blocked off the EGR to try to track down a problem. I'm sure you have reset the computer after installing the resistors, but if you haven't, that's something I would do.

 

Okay, I put the EVP sensor back on and that cleared all the EGR trouble codes. Then I disconnected the battery for about 20 minutes, reconnected it, and drove the truck for about 40 minutes. The throttle still hangs. The only code(s) I get now is 212, 412, and 411. I'm guessing the 412 and 411 are related to 212(Loss of ignition diagnostic monitor signal to PCM or spark output circuit ground).

Any ideas on where to start looking? I know I can fix this if I knew where to start. I've already cleaned out the plugs and did the electrical checks on the ICM harness that where in my Haynes manual.

I don't have the money to keep replacing parts or take it to a dealership.

 

Try to contact fefarms on this board. He is very knowledgeable about the electrical aspects of these trucks and can probably help you better than I can. The only thing I can think of is that the in-line resistor in the IDM circuit could be burned out and causing the code. It's buried in the harness somewhere.

 

If you get code 212 and there are no other obvious ignition problems, it is possible that the 22K ohm resistor in the harness is broken. The main ignition wire comes off the TFI module, goes to a splice in the harness about halfway back to the PCM. From there it splits three ways. One wire goes to the coil primary negative terminal, another goes to the dash to run the tach. The third leg is a 22K ohm 1/2 watt resistor soldered into the splice. The other end of the resistor goes to the PCM and becomes the "IDM" signal. They put the resistor in the harness to protect the PCM from the high voltage inductive transients as the coil primary is switched by the TFI. The resistor is fragile, and easily broken in half if you try to flex the harness in a zealous search for intermittent shorts or other problems.

The other possibility is that the SPOUT jumper is open or missing. The computer checks that IDM is present with the engine running, and also that spark timing is advanced under the control of SPOUT coming from the computer. Hook up a timing light, rev up the engine, and see if timing advances. If it is stuck on 10 BTDC, SPOUT is not working.

In my experience, a broken resistor results in code 212 and no other adverse symptoms. The computer doesn't seem to use IDM for very much, other than for diagnostics -- checking that the TFI is actually firing the coil and that SPOUT is able to vary ignition timing. The computer's primary input is PIP.

Code 411 and 412 are KOER codes. They mean that the computer does not seem to have sufficient control over engine RPM (fast or slow) during the engine running test by using the IAC. The computer expects to be able to close up the IAC and see 500 RPM (it uses PIP to judge RPM). It expects to be able to open up the IAC and see 1500 RPM or so. If you have a bad vacuum leak or the throttle blade is hanging up, then the IAC has too little influence on incoming air, and even when the computer pegs the IAC in either direction, it can't get the RPM under control. If the IAC is not functioning (blocked up, electrically disconnected, an open circuit), then similar results will ensue. It is unlikely that code 411 and 412 are related to code 212. If there were problems with PIP, the computer would not be able to control fuel injection properly, and the engine would run really bad, or not at all, -- not just have an idle speed problem.

The combination of code 556 and code 212, in the absence of other symptoms of problems with the fuel pump and ignition, may indicate corrosion in the big 60 pin connector going to the PCM. Pull it off and visually inspect.

 

Thank-you very much. I know the spout is working as when I unplugged it, the engine ran different. I also checked it with a timing light. The PIP sensor was replaced a few weeks ago when I couldn't get it running. I found out it was the ECM/PCM capacitors. But, while I was at it I also cleaned out that huge plug. And, I did inspect the whole harness(moving wires around alot) so I probably did break that resistor. I have a 22k 1/2 watt resistor on hand so I will inspect and replace that.

As for the possible vacuum leak, I might have a few. I forgot to block off the vacuum lines for the solenoids.

I'll let you know what else I find, do, and the outcome. Thanks again!

 

Well, I check the resistance from the ICM to pin 4 on the harness to the PCM and I get 21.8k ohms. That seems fine. Then I went and blocked off the vacuum lines. After resetting the computer, the truck still hangs the throttle and I still get code 212. Codes 412 and 411 dissapeared. But, I now also get code 327(EVP below minimum voltage). I feel there is no way to win with that stupid EGR circut.

Can the thermactor tubes leak when disconnected? Could they cause some sort of air or vacuum leak? Or is it possible the computer is changing settings when it expects the thermactor system to function(rapid deceleration, suspended rpm)? I will be tearing the rest of the system out and pluging off everything permanentally this weekend.

All and all, the truck runs great. I just need to solve this hanging throttle problem. It has much more power than it used to(alot of cheap, and good, mods). It now has better gas mileage under normal driving conditions. After I hit 15mph, it feels like my dad's 2004 F150 with a 5.8 acceleration wise. My truck's powerband kicks in at around 2,000 rpm wich I figure is about normal for a 302.

 

accidentally double posted

 

Well, after driving it today, the problem is not nearly as bad as it used to be. It now only hangs for a second or less and only above 30mph. The truck now idles better, shifts better, and doesn't seem to be running rich at idle anymore. All I did was plug off the extra vacuum lines for the thermactor and egr system.

However, a new problem as came up. When I start to move from a stop, and if the throttle gets blipped, the truck stalls. Any ideas why it does this?

 

First verify that the main throttle closes fully and reliably. Put an extra spring on it if you have to. Check that the throttle cable isn't frayed and hanging up.

Next, check the TPS voltage at idle. It should be around 0.9 volts. Advance the throttle (key on, engine off). The TPS should rise smoothly from 0.9 volts to 4.5 volts without any dead spots.

The computer opens the IAC all the way at cruise. This allows it to close it slowly when you let your foot off the throttle. This simulates the action of a dashpot and prevents excessive manifold vaccuum and attendant emission problems.

The computer also uses the IAC to act as a "stall saver". If there are any issues with the TPS, the computer may be confused about how to operate the IAC, thus the stalling and "hanging" at high RPM. Alternatively, the IAC may be sticking or blocked with carbon. This would explain the stalling and hanging. It is possible to clean the IAC and improve its function. Do a search on "clean IAC".

 

I recently cleaned the throttle body out. The springs and cable function fine. I've also checked the TPS more than once. It shows .89 volts at idle and rises smoothly to 4.47 at full throttle.

I've read about adjusting the TPS minorly by loosening the two screws and turning it just a hair untill it reads 1.0 volts(the screw holes are supposedly bigger than the screws). Could that be why my idle is lower than it used to be?

And, as I stated before, I cleaned the IAC out very well. After I did that, the truck idled a little smoother, but the throttle hanging was the same. Checking it with the ignition on/engine off, I got right on the dot resistance and reference voltage. Is it possible the plunger itself has just gone bad? I'm not sure what its made from but I'm guessing its something that will wear and deteriorate.

BTW, I did the KOER test again and I got 412 and 411 again. With that information, I'm guessing the IAC has worn out. I'm trying to not spend money when I don't have to(very tight budget right now).

 

I'd replace that IAC... It's still throwing codes even after it's been cleaned. Pull the electrical connector off of it while the truck is running, it should stall..

 

Replaced the IAC, problem solved. Thanks everyone!