318, 145k, runs great, then at any speed it starts shaking, floor it and force a downshift and it smooths out; seems to run better in cruise but still shakes; had the trans checked (no problem); tune up (3 times) routed wires so they weren't crossing (no change); replaced IAC motor (runs better, but still 'clicks' and starts shaking, then 'clicks' and runs smooth); not suspension related, let my foot off the gas and it rolls smoothly; been dosing with Seafoam; seems to run better when it's cold; surges mildly at idle; gettin 27 code (ignition control system);
Where is the IAC sensor located? I'm ready to drive it over the side of a cliff. Had it to 3 mechs, none of them seem to want to spend the time to truly trouble shoot it, but they still charge me $500 and tell me "it's still doing it".
Help!

 

First off forget about IAC anything. IAC stands for Idle Air Control and only comes into play at idle with your foot off the gas. It will not cause the problems you've described.

Your problem is one of four things, the TPS (Throttle Position Sensor), the crank sensor, the cam sensor (pick-up coil), or the engine computer.

 

Do you have a power inverter plugged into the vehicle? What you had described has happened to my van just like that. Inverters that run on a SINE will cause the PCM (computer) to mess up the tranny.

If you replaced the replaced IAC motor, then why are you looking at the IAC again?

 

Originally, the Intake Air Control Motor was frozen with carbon.
I cleaned it, lubed the shaft, put it back in, and it seemed to make the difference. It started shaking again after a week or so (possibly change in outside temp); I replaced the IAC motor, but this time it didn't make a difference. I figure, there has to be a sensor somewhere in the circuit that reads intake air temp and informs the computer when to open the IAC motor; that's what I was looking for.
Today, I purchased an auto stethoscope, and it appears that one of the injectors may not be working. I am taking a leap and changing it out tomorrow, so I'll re-post if that solves the problem.
I have thought that it could be the computer, although as I said earlier, I have gotten a 27 code which I looked up on this forum and it seems to be related to the injector or the wiring harness. It's possible the seafoam was making it run better and I thought it was the IAC motor. (I get it that it relates to idle).

 

had a 200 + mile round trip and it shook the whole way. I changed out the injector that doesn't sound like it's clicking, and the new one is no different. Then, yesterday, it decided to run incredibly well all day. Not a single relapse, but that is what it's done in the past. I kept with it and changed out the TPS, the MAP, and the crank shaft position sensors ($195.00, but still about what it would have cost me just to pull it in to the dealer). It was still running great last night, got my fingers crossed. Making another run to Portsmouth today, so I'll see how it goes.
COTV business always comes first.

 

That's what they charge around here, $195 just to pull it in. Then there's a diagnostic charge, then labor, then parts, and then of course taxes.

 

of the 94 Ram vAn. Nothing I have done so far has had an impact.
Yesterday, I got three codes: 12, 14, 27.
14 MAP related, so I discon the battery and let the PCM reset.
27 is Injection Control Circuit, and I have not a single idea what that means. I visually inspected wiring harness, etc. Nothing visibly wrong.
12 is power to PCM disconnected. But, I had not at that point disconnected the power. Someone suggested PCM is faulty, and since it was reading a loss of power I am now assuming this to be the $199.00, culmination of a 12 month search for an answer. Of course, something has started whining in the front of the engine (155k), so now I will probably fix it and it will blow up. Not that I'm whining, but I am questioning the sanity of trying to keep an older vehicle running.

 

Not sure this may help or not but check the vacuum lines between the engine vacuum canister valve and the fuel vapor canister. On your van the canister is behind the front right tire under the door of the van. And the valve should be on top of the left rear side of the motor. Make sure it is connected tight and the lines are in good shape. I am wondering if the shaking is related to the purge valve cycling and drawing in to much out side air.

 

thanks. I'll try it.