[NssJ]

00 Ram Van B3500 5,2L with a P1294 code.

Recent History:
Had stalling issues with NO BUS, then P0505 would come up when it would run again 10 min later. Removed IAC valve to clean it, but it was rusted and pitted, so replaced it. Cleaned IAC mounting port & throttle plates. Replaced plugs, wires, & coil as mentioned on here under NO BUS threads. Also replaced PCV and breather valve.

With the above parts replaced, it ran better than before. Plenty of driving in past week or so, no stalls, no codes until today. Seems to be running fine, though right before code came on, I noticed I had to stay on the brakes through a school zone as it wanted to do more than 20mph on its own. Noitced similar symptoms on P1294 thread on here, but most of that thread was on toyota's w/ elec throttles... no real useful info for an old school V8.

Where should I start looking?

 

[NssJ]

Now that I think of it, the van accelerated on its own before the tuneup as well. It accelerated more than I would assume normal without gas pedal when I tested the brakes. Just never saw this code til now.

Everything is connected where it should be to the best of my knowledge.

Ok, here is where I'm at:
Blue: is areas I directly checked and were good. No leaks around intake manifold gasket, no leaks on blue lines, vacuum present and engine change where blue connectors were disconnected, ie working normal. Don't see cruise control on diagram, but its lines and connecters didn't react to spray. Both sides of PCV & brake booster line are normal.
Yellow: Did not check. I checked all of HVAC under center of dash, but a few lines went off behind glove box I didn't get to. Moved all HVAC controls to all positions, no change in RPM. Also, gas tank is full, so can't access on top of it now. Did not drop EVAP cans, but sprayed a lot on top.
Green: No Vacuum present, no change unplugging them. The EVAP vent did nothing when sprayed directly. the service port did nothing, and the rearward line off purge solenoid had no vacuum or change when disconnected. I'm guessing since neither of those did anything, they pretty much cover all the gas tank lines I couldn't get to anyways. I'm assuming they only get vacuum(or leak) when that purge solenoid activates anyways, so probably normal operation.
Orange: I'm not sure which is MAP sensor. Front of throttle has one vacuum line only for EVAP. Rear has IAC valve, drivers side has 2 sensors, unsure which is MAP, both appear flush on throttle, no vacuum line there anyways...

Red: possible leak. I went through 1/2 can throttle cleaner, full can starting fluid, 1/3 can brake cleaner. Tried someones dumb idea of WD40, but that's way too flammable near exhaust... I sprayed every line and fitting except glove box area, and over gas tank. Did water once I ran out of chemicals.
Out of all that, I thought once, the engine changed speed where I have circled red. All 3 of those lines are in the valley between intake man & drivers valve cover. Thought engine bogged down once while spraying there. Removed all the plastic wire loom shields(grey outlined) off those 3 lines, sprayed again, and bogged once (I think). When I moved lines out of the valley, none would set it off sprayed individually. intake manifold under them wouldn't do it either. I'm not even positive I heard anything, it was barely a change in RPM (my imagination?). Can't feel any cracks or see any problems on lines. Seems 98% leak free, real hard to tell so far.

I reset the code for now in case it was just a fluke incident, but I'm guessing creeping forward up to 25mph without gas pedal input is not normal. Still does it today without a code present(yet).

What should I check next?
Also, can I just cap off some of these lines right at the intake manifold to test everything but one section at a time? Or will that cause any vacuum issues to interfere with troubleshooting?
Can I run a short hose to bypass the EVAP solenoid(like a constant completed circuit) to check vacuum further back on EVAP lines that didn't have vacuum previously without solenoid on?
Would butane or propane make a more noticeable RPM change on a leak?

 

[NssJ]

A fairly common internal vacuum leak can occur underneath the intake manifold. It will draw air in from the crankcase.
An easy way to check for this is to remove the pcv valve and breather filter from the valve covers and block off the holes on a running engine. If you notice a vacuum developing at these holes after a moment, it usually means that the intake gasket underneath the manifold has failed.
There is a sheetmetal plate bolted to the underside. The manifold has to be removed to service this plate gasket.


Ram_Plenum06.jpg

There wasn't vacuum. After holding a few seconds, once I move my hand, they blew air outward; either side, whichever hand I moved 1st. Held paper over it to double check, it blew the paper away when i let go.

 

[NssJ]

Phew is right. I didn't wanna sound like I didn't like your answer, but I'm glad its not that.

Not sure if it has leak detection pump, maybe on far back with gas tank, or maybe accomplished by whatever that evap solenoid is? I'm guessing the 2 times I thought idle changed, I had just sprayed enough of a fume cloud for it to suck over the lip of the throttle... I heard soapy water shows more, so I may try that again.

There were 4 vacuum trees going off the intake. I capped off one at a time to see if it changed. Brake booster line made it idle a little better, so replaced that hose. No other lines changed anything by being capped. Capped off all 4 at once to see if it was maybe bad on more than one branch, No change. Also, found map sensor is on the front, but its plug is on the side, next to what looks like a throttle position sensor. Still map sensor appears flush mount, no vacuum line.

I just put a new IAC in for a P0505 (old sensor was rusted and pitted bad). That code went away with it. Though this didn't have a P1294 til now, It over-idled before the IAC too, so doesn't seem like IAC did anything with this issue, just its own code cleared.

Can I unplug the IAC to see how idle changes? I'm guessing it would go to some kind of default limp values until corrected, but would it idle better possibly if the new IAC wasn't working right? Can it be installed wrong? I took it from box, careful not to move tip of it, and put it right on the throttle.

 

[NssJ]

Possibly dumb question: should I have used any rtv at the base of the IAC when installing it?
It seemed like it had a rubber o-ring built in, so I didn't add anything.

 

[NssJ]

Ok, pulled IAC, checked key on/key off, the IAC moves. Started the engine and IAC tries to move fully out to block (its own( leak. Seems normal. I had the battery disconnected for 10+ min. Cleaned IAC port and the face where it mounts again. Reinstalled, batt reconnected, code gone. After a few minutes, while it was learning, I heard idle go back up to how it has been; it still accelerates on its own too. I'm sure code will be right back. Will retry spray leak check later.

I read on another Dodge forum,
"Also having really worn spark plugs could set off this code since the engine needs to rev higher just to stay running."

Is it possible a plug not fully seated could do this too? Front 2 plugs were hard to tell if fully seated when I put them in. No really good angle to ratchet from... Wouldn't this set off some kind of misfire or ignition code too?

 

[NssJ]

I'm still trying to find someone with a free/cheap scan tool to check. Autozone and such said they have code readers only, so they can't give me any more info than the Van already does itself. So no luck there at the moment.

From the wording of that, sounds as if a TPS or MAP sensor code would override and prevent P1294, if either of them were bad.

1. Checked throttle operation, no binding by pedal or throttle, springs back well. plates look fully closed.

2. Looked down into throttle with lighted mirror. Throttle plates look good. I cleaned with spray and a toothbrush when I replaced the IAC before. Inside of intake looks really clean. Tiny traces of oil in the bottom, like where vacuum lines brought a little in. Looks cleaner than I expected.

3. Unplugged battery for 10+ min. Unplugged all 4 vacuum branches and put rubber caps over intake side to seal off. reinstalled air cleaner and drove. It still idles too high, accel on its own. Will only get up to 15mph vs 25 before, but still rushes up to 15 quickly. Sprayed all 4 caps with soapy water to make sure no leaks. Also removed one cap at a time, noticeable vacuum & idle change. So 0 vacuum leak there still pretty much the same problem.
Like this I noticed something. In P or N, van idles a little higher, like it normally would. In Drive, it drops down to what sounds normal. Van would slowly accel from 0-5mph. Once it hit 5mph, the idle jumped up like in neutral, and the van started accelerating a lot faster. It's like once it starts rolling, the engine thinks its not in drive and bumps up the idle.

4. Sprayed all around intake edges with soapy water. No bubbles, no idle change at all. Sprayed all around base of throttle body to check its gasket. No noticeable leaks.

5. MAP sensor:vacuum port #5(other 4 still capped off), Unplugged MAP, idles higher, P0108 code, disconnect batt, uninstall MAP, put rubber cap over its vacuum port: van won't run, starts for a sec, but won't stay on. Plug MAP sensor back in, but leave vacuum capped off. Van idles high, P0108, but it runs. Regardless what I did with it, it behaved close to the same, just added obvious code. But sensor, and short hose under it both appear good.

6. Finally found throttle adjuster screw where hinge rests at full close. screw threads poking out backside. Front side has kind of like a small freeze plug hiding screw head, which I'm guessing is the sign that no one has tampered with that screw.

Read somewhere aftermarket IAC's don't work so well in Dodge's... May order a factory one if I can't find anything solid wrong.
Shot wires for it.
IAC pinsuter to outer 50ohms. inner to inner, 49.5ohms. Both normal.
Wires, IAC to PCM: purple and yellow wires had 0ohms resistance. Grey and brown had 0.1ohm and 0.2ohms. All under 5ohms as req.

 

[NssJ]

New Mopar IAC installed, but only got to run it 5 min before coolant leak became a serious issue. Didn't have time to fully warm up, let alone relearn the computer, so unsure at present.

Found this while reading timing cover threads:

"For the timing gasket, although there was no oil or AF leak, if air were allowed to pass through this gasket gap, it
messes with the crankcase/PCV system vacuum. This could've affected the way the engine ran to some degree."

Wonder if that could be the vacuum leak I couldn't find... I'll know when gasket is redone, though unfortunately I won't know if it was the IAC or that for the fix.

 

[NssJ]

Ok, 1294 is back. I had like 6 days of good driving after timing chain stuff done. Idle sounded lower/better. Still would accel itself, but slower, and up to about 22mph. All driving was relatively short trips, probably 12-20 trips.

One thing that stood out, it didn't come back until it got cold out again. Drive in 32* weather and it sets a code within 2 min....
Unsure what would only act up in cold, or if it just took so many trip cycles to set it.

While doing timing chain, noticed, previous whoever snapped off passenger front bolt of intake manifold, then just set the half bolt in its hole. I put a good amount of rtv in the hole and put the half bolt back for now. I'm gonna recheck pcv grommets for suction, then spray leak check that corner of intake.
Seeing how many hoses on my 2003 GMC dry rotted this week, I'm gonna assume everything rubber on a 00 van could be leaking by now. Will start with cheap/small pieces first and work through vacuum lines.

MAP sensor elbow, charcoal canister elbows, brake booster hose adapter thing... are those dealer only pieces, or somewhere cheaper to find those vacuum hose elbow fittings?

 

[NssJ]

Ok, I think I got lucky. Haven't seen code return in a few weeks. Haven't had time to do a run and see how fast it will drive on its own though.

From autozone, got vacuum plastic Y fittings, hose reducers and a few size hoses. Made a ghetto evap fitting to replace the splitter elbow. Also, they had a 4 pack of small elbows, trimmed with a razor blade and made a new MAP sensor line. Not sure which fixed it, nor really care at this point. no code, and idle doesn't sound horrid fast anymore. $20 worth of assorted parts was a pretty good fix.