I've been messing with this problem for a while on my 87 F150. It has an EFI 4.9 (Walk softly and carry a big 6, lol) and the 4-speed manual with OD. When you start it in the mornings, the idle will shoot to 2,000 RPM or so for about 30 seconds, then back down. The problem, besides that, is that since it's gotten colder, the idle will drop lower and lower until it stalls. It always starts back up, but it shouldn't behave like that. I also notice, on first start up, there's some black smoke (just a little) indicating it's running rich.

So far, to combat the problem, it's had 6 new injectors (not my doing), a new high pressure fuel pump (on the rail, again, not my doing), and the rear in-tank pump (you guessed it, not my doing...), new IAC (my doing...), new TPS (me again) and I've checked for vacuum leaks. I checked for codes but I'm not sure I did it right (GMs are SO much easier to do this with, Ford really dropped the ball with this setup) and didn't get any.

I'm about to replace all the vacuum hoses, as they all look dry rotted. And I'll look into/do whatever y'all think I should...to include playing in traffic, lol.

I just want her to behave right again...like she did years ago (truck has been in my life since 1993). She was my great grandpa's truck and I want to keep her in good shape...thanks guys!

Edit-forgot to add, occasionally she will develop a surging idle, like at a stop light...and I've found (don't jump me, I know it's wrong to do) that if you turn the ignition off and back on real fast (without killing engine), she'll normally straighten out for a while...


new information here: so the other day (Sunday) I ran the codes, I had codes 23, 67 and 95 (defined down in a reply)...thought they might be old codes, pulled the negative battery cable for a few minutes, put it back on...idle was rock solid. Truck has been running great until tonight. I get in 'er to leave work, start her up and let her warm...she jumps to 2,200 or so to warm up as normal...after about 30 seconds she settles into an idle, idling good. I get to talking to a friend as she's idling...then, it happens. She started surging again...BAD. Eventually stalled. After starting again, no surge...for a while. Then it came back. Ran codes again...same damn codes are back...23, 67 and 95. It has a new TPS, 2 new fuel pumps (hi-press and one in-tank) and various other things. I'm wondering if my EEC is going bad...anyone have any input? I'm lost, please help!

 

So, y'all are telling me, out of all the intelligent guys/gals on this site that know Fords like I know the back of my hand....no one has any ideas on this problem? I guess I'm the first 1987 F150 with a straight 6 to have an idle issue.

Sorry, I don't normally bump a post, but it just shocks me that no one has any input on this problem...

 

You've covered the bases pretty well.

How about an O2 sensor? Only thing you haven't mentioned, and could cause the surging when warmed up due to misreading and causing computer to keep changing.

Just a thought.

 

With it being a Holiday weekend, I doubt everyone on this site was just sitting and waiting to answer your question immediately. You need to give people time before you jump on their butt.... they ain't getting paid to be on standby to give free advice...

 

White 97, you're absolutely right...and I apologize to everyone who reads this. I'm just a bit frustrated and want to get this thing fixed. I did mean to "bump" it so people could see it (it was on page 3 already) but I didn't have to be a jack@$$ about it...

FreightTrain...you're also right. Not sure why I didn't do an O2 sensor...I'll do that next...not sure she's ever had one so I know it's time. Also gonna jump on replacing those vacuum hoses sooner rather than later, like I said, they all look dry rotted....

 

It does sound like the bases have been covered pretty well so far.. O2 sensors are not cheap, but if it is original to the truck, it is probable due for replacement.

After you check/replace the vacuum hoses. (just do one at a time, so you don't miss route them) Use some spray carb cleaner to check the manifold connections.

You mentioned surging at idle, I'm wondering if you have cleaned the IAC (idle air control) or replaced it..

 

The IAC has been replaced...but I'm about to go try something...I thinkSteve83 might have stumbled upon the problem...something I had tuned out...the infamous hissing brake booster...gonna go plug off it's vacuum supply and see if she straightens up. I feel so dumb for not thinking about that. Oh well, probably gonna do O2 sensors too...all that stuff needs to be changed, I just replaced the original heater core/heater hoses/clamps yesterday!

 

ok, update...PROBLEM FIXED! i feel stupid, but at least i caught it. with these older computers, they don't update themselves...such as when you replace a part. well, over the last year and a half, she's had 2 fuel pumps replaced (with a section of wiring repaired) and a TPS/IAC replaced...the battery was never disconnected/discharged. so, today, i suspected those were old codes, and pulled the negative battery terminal for about 10 minutes (cleaned it too)...hooked it back up, and her idle has been ROCK SOLID where it should be ever since (about 2 hours of KOER cycles and a few trips)

turns out those old codes were changing the way the EEC functioned. i figure it was seeing the TPS was out of range and was reverting to basic parameters to make the truck run.

oh, and here's a weird one for ya...ever seen an EFI truck born without a Check Engine light? mine was. i went to pull codes earlier...saw no blinking light...so i pulled the dash bezel expecting a burnt out/pulled bulb. looked in the sun to see where the check engine light should have been...looked in the dash...no bulb, no socket, no wiring behind the gauge cluster. we've had this truck since 1993...it was all original/perfect when we got it...that light wasn't removed. it was never there...i used my test light to retrieve codes...odd huh?

 

Please read the bold text in the first post...I'm begging...I need help with this so badly...help me fix a wonderful truck!

 

Wow I have this exact same problem and it drives me carzy! My does it more often than not but my goes up the 2500rpm. If I tap the pedal it stops, idles fine for a little while and then the idle with start to surge and the it will die. I have all new vac lines, new IAC, TPS, O2 sensor, Ignition mod, coil, and on the fuel system the only thing that is not new is the selector valve and injectors ( I get all motorcraft if I can afored it, if it is not motor craft it is bwd). I was getting high voltage codes for the EGR ( te valve and sensor is new also) so I pluged it and it helped the surging some but not the high idle upon start up. After I get her going the only thing that happens is some small surging at a light or something but I dont notice it unless I look at the tac. I also have a hissing brake booster that I hear in the cab after I release the brake but that has been like that for a few years. If I fix it I will let you know. Good luck on your tuck .

 

I know it is suppose to go up to 1500rpm to help the truck warm up but my doesnt do that any more. Also mine will idle at 1200rpm after I drive a minute or two then it will go away.

 

Even though you have a new TPS, check the values on it, I had a new aftermarket one that was .02 volts off, enough to screw it up, especially when it warmed up. Chased it for good long while. Especially if someone has messed with the base idle screw/stop. The computer was reading just off idle, enough to start opening the EGR and ramping up the fuel at idle.

Fuel Injection Technical Library » Throttle Position Sensor (TPS)

 

Something I've found helpful to do is unplug and clean all the electrical connectors for any engine-control and/or EFI devices. I use electrical contact cleaner (that's safe for plastics) and a small file, sometimes a piece of sandpaper wrapped around a screwdriver.

After 25 years, water, road grime, magnesium chloride, etc. can make their way into the connectors and cause corrosion.

The rubber/plastic insulation on wires will dry out and crack if exposed to high heat for a long time.

Also, ensure there aren't any vacuum leaks anywhere - depending on the environment, rubber hoses can deteriorate & crumble.

 

I checked it about a month ago and it was at .7 or .8 at closed throttle ( It has been an on going thing for a while now). It is like it forgets the throttle is closed and the realizes it that it really is closed and gets back on track. On the I6 TPS there is not a place where you can adjust it. It only goes on one way and there are two mounting screws.

 

I will try this the next chance I get.