VickMacky

I hate starting new threads but I just can't figure it out. 94 351 4x4, is it normal? When first started cold, It will idle at ~8-900 in gear and should go down when it's warm but it doesn't unless I bump the gas. If i make a stop and restart it, it's fine and idles at ~650. If i wait a few hours until it's cold again i have to do it all over. I replaced the TPS this past Sunday (Motorcraft) and verified .97-.98v closed and 4.62(ish) open, before installing TB back. It's ran perfect until today. Now I need to bump it to get it down or restart it.

TB is clean, IAC is new (not Motorcraft), no codes except 111. ECT sensor is new (not Motorcraft) and O2 sensor is new (Denso). I'm just at a loss.

Rusty but trusty

It never comes down on its own? Mine idles high when cold for less then a minute then comes down. I bump the throttle to get it to drop when I don't want to wait. No idea the RPMs tho, I have no tach.

VickMacky

Well it did since Sunday after replacing the TPS and unplugging the battery overnight. It did just as you said, it would idle high when cold then within a couple miles if I come to a light it was a perfect idle (~650-700). Now I can get in it after work, drive home (12 miles) and coming to a light it idles at about 850 or closer to 1250 in park (when warm). As soon as I bump the gas it comes right down to normal idle and stays that way until I let it sit for a few hours or more.

My MPGs have sucked too compared to others I read, mine is normally just under 12 with a good mix of hwy/city driving. I know just from the few months of owning/reading about these trucks is that they can be finicky using anything other than Motorcraft sensors. The O2 and ECT are aftermarket (albeit quality), I wonder if that would be an issue? Maybe I should adjust the TPS to read a little lower at closed throttle?

wde3477

Coupla suggestions for consideration - clean your Idle Air Control (IAC) solenoid. This looks about the size of a roll of quarters and straddles the throttle butterfly. These were prone to fouling during the Gen8s, and while the typical symptom was a surging idle - couldn't hurt to have a look. Carb cleaner works well to clean it out, four Phillips-head screws and an electrical connector involved to get it off.


Inspect the throttle butterfly area. Again with the gunk, it may be that buildup is preventing the plate from resting on the stop screw. Do not adjust the stop screw.


Perhaps another thing to check, thrown in at no extra costs :-)~, is to ensure that the linkages and cables move freely without binding or rough spots.


Not sure about the relatively later years, mine has always gotten around 9-10 mpg around town, 13 mpg on the highway tops. Guessing it has something to do with the aerodynamic efficiencies of a brick wall...


Hope this helps, and keep us posted on findings.

fltdriver

When you put the TPS on you did put it in then rotate it until the holes lined up to bolt it back on. The TPS must be installed properly otherwise it will cause problems. As for non motorcraft sensors I've never had a problem and almost everything I've replaced has been with the best deal I could find on brands that I trust.

VickMacky

Thanks for the suggestions guys. The IAC is new, about 3 months old. It's not Motorcraft so I don't know if that matters. The TB was cleaned thoroughly about 2 months ago. I haven't adjusted the stop screw but the plate has never rested on it. It's about 1\16th away. The butterflies are clean though and they close ask the way as far as I can tell. The throttle cable moves freely but I did add a small piece if electrical connector just behind the petal to take the slack out of it from stretch over the years. The TPS was installed retarded and turned clockwise to contact the butterfly tab. Voltage was correct but I wonder if I should adjust it closer to .90 at closed throttle?

fltdriver

Try shooting for .95 first, if the RPM's are lower after that then adjust slightly again until you hit the proper idle RPM's.

Chris_1

iTrader: (1)

Temp sensor good ?

VickMacky

Oh forgot, yes ECT is new but not Motorcraft. It a Delphi sensor. Being new I didn't test the voltage but I probably should. I replaced it about a month ago along with my thermo, radiator and coolant.

choate

Now I don't feel so bad thinking something is not right w my truck. It gets about the same as yours. The avg is usually about 11.5 highway/town mix. I remember when i first got the truck and drove it home I thought it was a super windy day. Then realized I'm driving a square box 70mph lol