I am having a slight stumble upon startup. It isn't reflected of the temp or engine temp. Actually, after the engine is warm it seems a little more pronounced. The engine fires to life with the turn of a key but it seems to initually rev to 700rpm for about 1/2 second then down to 500rpm, sometimes as low as 250 and then the idle stabalizes or goes into cold warmup. This has been going on for quite some time, maybe even forever, and I have just been ignoring it. The engines does this probably 95% of the time. Last spring I did do a tuneup consisting of new dis cap, rotor, spark plugs, wires. Im wondering if my coil could be getting old. I didn't replace that. Or maybe fuel regulator. I did change the fuel filter so that should be good too. Any help would be appreciated. Thanks

Oh, Beatie, here is one post for you.

 

What year truck / size engine?

Your coil might be going, but that would be more pronounced at 3000 rpm than it would at start-up. Your regulator wouldn't do that either. The only thing I can think of that has an effect on idle at start-up, but doesn't affect drivability, is the IAC (Idle Air Control) solenoid. Have you cleaned and/or tested yours?

 

sorry about that, I thought my signature was working, guess not. The truck is a 90 f-150 with a 302. In the past I have cleaned the IAC when the truck wouldn't idle without constant throttle. That was this spring, guess I didn't think it could be crummy already again. I will clean it out today and see if anything changes.

Also, once in a while the truck will fire like its going to start but instead of choking around 500rpm it dies. Then when I go to start it it cranks for about 1 second and I need to apply a little gas pedle in order for it to start.

Thanks, Cody

 

You need to check your fuel pressure, and check how fast it bleeds down after the key is turned off. This sounds like a fuel pressure problem. Not necessarily the pump, either. I'm thinking you're not maintaining pressure at start-up, which could be a leaky injector, a bad regulator, or a cracked hose inside the tank. Get a gauge and test the pressure and the bleed down time.

Take care,
~Chris

 

I think I solved the problem...for the time being. I cleaned out the IAC and now it starts up and idles better than it ever has. But I also made one of those home grown FIPK's at the same time so that could be somewhat to do with it also. The wierd thing I found out was there was a little piece of aluminum pop can that was obviously used to restrict the air flow on one of the 2 wholes going into and out of the IAC. It was covering one whole with about a 1/8" to 1/4" whole poked through the aluminum!! The last time I cleaned the IAC i just left it in place thinking whoever did it must have had a reason and I didn't want to mess up my idle since it idled fine when I bought the truck. But since removing this aluminum restrictor the truck now idles upon imediate startup 100% better than it ever has. The truck also revs much nicer and has a little growl to it at higher engine speeds which I attribute to the custom FIPK. Maybe I can get a few pics if anyone doesn't know how to do this. The crankcase breather I just kinda left out in the open, I hope that's OK. But I can say im definately glad I didn't spend 200 dollars on something like that.

 

That's weird...I wonder if the previous owner took it to a shop and the shop put the pop can lid thing in there so they could tell him something need's to be replaced and pay us $$$$ to do it.....I've seen places do stuff like this...one place even wrapped my throttle cable up a little making it idle higher...you should have seen the look on there faces when I popped the hood and found this.

 

yeah, funny thing is it used to idle just fine....who knows.