Hello. I have a very specific high idle problem with my 1994 vans 5.8 Windsor engine. It has 285k miles on it and otherwise runs like a champ. When I start it up, it runs fine at a higher than normal idle to warm up, then automatically throttles down. When I give it gas, and let up, it doesn’t return to the same idle. Even when I drive and I let off the gas, it doesn’t return to a low idle. It’s at about I’m guessing 1000 to 1200 rpm. Here’s the weird thing- if I put it in neutral and tap the gas pedal, it throttles down. It’s very predictable. With that many miles on the van, I’ve replaced several sensor etc. Even the PCM when I first got the van because nothing else worked to solve a rough idle. The computer changeout solved that problem. It ran great for many miles but after a long trip, when I pulled over at a rest stop, it was idling really high. Cleaning the Throttle body solved the constant high idle but never solved the problem I mentioned. Any help would be appreciated.

 

Have you done any work on the idle air valve? I read 5.8s need the right IAV. It’s not one size fits all 5.8s.

Sixto
07 E350 5.8 190K miles

 

Could be any number of things, vacuum leak IAV, TPS, ECT sensor, PCM, Start at the easiest thing you can do and that's see if there are any codes stored, next would be check for vacuum leaks, then check the voltage on your TPS You may have to re-clean the TB, if the Door is sticking a bit, could be dirt, corrosion, varnish. All those could keep the idle raised. If the ECT isn't functioning properly, (Incorrect reading Low) it could cause it to think it's not up to operating temp.. You need to do a full diagnostic.

 

Thanks for the reply’s. I’ve replaced the IAV about a year ago. I’ve recently replaced all of the EGR components. The TPS is clean as a whistle from the work done before. The flaps work perfect on the throttle positioner and have absolutely no restriction. Hard stops when fully closed. Got to see look at the other parts mentioned to see if they have been replaced. Got to match name with the pic of the part. Give me a few minutes.

 

Currently tracking the sound of a vacuum leak! Will keep you posted!

 

I recently dealt with this same problem on my '93 w/5.8 and it was the TPS.

The symptoms also included rough shifting and there was a code (122 or 123?).

Now, when started cold the idle is higher than before and higher than I'd like to have on a cold start.

Tapping the throttle a bit will bring it down. So need to do some more fiddling.

 

Was following Mike1’s advice. The TPS was next on my list. I’ve replaced most of the sensors and control valves on the vehicle at one point in time or another. My van is running great and shifts good. Question. So you had exactly the issue I’m having along with a few others? Reason I ask is why I’ve been replacing all my sensors and control valves. My van has 189k miles on it and them old parts are bound to go bad so I don’t mind throwing parts at it as long as it’s low dollar stuff. I’ve spent probably $$300 so far on sensors. Maybe a little less. It’s a camper van and we’ve been putting it on the road. Heading to Washington State on a road trip in a week. Just checked the price on the TPS. Looks like under 40 bucks. How much of a pain was it to come off? I don’t have a lot of room under the hood!!

 

I wouldn't change it unless you have a code. IDK...I guess I have a different take on replacing parts. Sure, they're all old parts (mine has 152k) but unless proven to be bad, what is on there is better than a lot of the aftermarket replacements. Unless you get OEM (usually Motorcraft).

That said, I did buy the TPS at Autozone for ~$40 but now second guessing that my higher cold start idle is due to that non-OEM part. Luckily, I'm just using the van for infrequent local travel at this time. In the past 5 years though it's been all over, including AZ to Alaska.

PS: I did get a CEL, so if you're not getting that, your problem may be different.

 

I agree with the OEM parts. Oreily’s offers a OEM TPS for about $70 bucks. I’m gonna get it. Don’t remember ever changing mine out. It seems like the most logical problem, now that it’s been mentioned by y’all. It’s a moving part that most likely has a potentiometer that can be measured with a meter once disconnected. I saw someone test the TPS while it was removed and still plugged in. It throttled the engine. Not sure if it was spring loaded but the fact that it was plastic and moves, tells that it could wear some. That moving part if worn where it sends the signal to the ICV, could be impacting the smooth transfer of information. Needless to say, I’m gonna eliminate that possibility. I wish the TPS was designed to be removed without removing the throttle body. Since I’m down there, gonna replace the water temperature sensor since that was mentioned. My justification for putting money in this van is that new camper vans cost upwards of 80k. My wife likes it and as long as I can keep it running good, I will never have to go there! I will keep y’all posted. Other that that pesky idle issue the 351 has been running pretty good. I may need to upgrade the ICV to a OEM also. That one is definitely after market. Got to start leaving the after market stuff alone but we’ll see.

 

I have a Bosch 1300 OBD1 &2 meter that I can’t use on this van because I lost the cigarette lighter cable. On the van when connected, it’s asked for it to be connected even though it has batteries inside it. I called the tech center and they said it won’t go any further in the diagnostics without it. This is only on the older vehicles. OBD 2 vehicles don’t need that cigarette lighter adapter connected. So I’m flying blind at the moment on trouble codes till I get the adapter ordered.

 

So here’s the update. I’ve replaced the TPS with a motocraft brand. Thank goodness at no cost since oreily took the aftermarket one I bought a year ago and gave me a motocraft. The bad news is it did not solve the problem. The next thing I took back was the Autozone idle air control valve. That gave me a new exchange. Bad news is it did not solve the problem. So I unplugged the new IACV while it was running and nothing happen. Your thought?

 

With 285k on the vehicle there is a very good chance the throttlebody is worn... or more precisely the butterfly pivot shaft bushings are worn and that results in the buterflies hitting the bores before they get the thier proper closed position and/or it causes an air leak around the bushings, both of which can result in a high idle. Another possibility is a sticking throttle cable.

 

Will spraying solvent around the throttle body reveal loose bushings?

Sixto
07 E350 5.4 190K miles

 

I thought it might be the cable because the cable was a little sticky when pressing. After I disconnected it at the throttle body, it was still sticky. It was the flaps sticking while running only. No sticking when engine off. I sprayed the pivot points with penetrating lubricant and it solved that problem but not the idle issue. Another thing. When I pat the throttle, it will idle high for an about 4 seconds and throttle down most of the time, but go right back to high idle once you press again. I think you are on to something regarding the throttle body. The flaps and TB are very clean and smooth and close completely but for sure pulling good suction still. Not sure why it would throttle down after a few seconds if that was it. At least most of time it throttles down. I was leaning towards the PCM but I replaced it when I bought the van about 20k miles ago. So TB replacement seems more likely. I also replaced the temp sensor. Is there more than one temp sensor?

 

Your post #11, you stated you unplugged the IAVC and nothing happened. When the IAVC is operating properly it keeps the engine from rough idling and surging, and keeping the high idle away, it makes it idle normal. If you unplug I would assume it would cause problems, You said it didn't, could your New IAVC be bad and you just over looked it because you had already replaced it?
When you unplugged the IACV was it before first start or was it already warmed up. When unplugging it it will stay at the same position it doesn't default to open or close so if you unplugged it a high idle position it would stay at high idle position until you plugged it back in and if something changed in the running condition of the engine the IACV would then try to adjust and compensate.
I also stated that you might have a vacuum leak somewhere. Didn't hear anything back on that, a lot of time it's the brake booster hose gasket that causes the high idle.
I myself think you're going down the rabbit hole thinking too hard about what's next on the list to replace instead of going back over what you've already replaced and looked at.