Idle dips & surges in park after tune-up. Any idea why?

[DerekTheGreat]

Hi everybody, welcome to Monday!

About two weeks ago I had my car in the shop for a bunch of little things. The only engine work done was the tune up: new plugs, wires, cap & rotor. Plugs are autolight platinums & the rest of the stuff is motorcraft. Ever since I got it back though I noticed several things are a little different.. First off is the main issue: Car starts up fine and initially idles smooth but then it starts to "hunt" for some reason. Doesn't stall but you can hear the engine rev up & down far enough so that the lights dim. Is the IAC bad? Car was fine before the tune-up. Once I put it in gear everything is fine though. What do you guys think?

Other things noticed:
Once started the car's idle calms down much faster than it used to, and sounds like it is trying to idle a bit lower than before. Shortly after it gets there it goes into the fits. Doesn't happen when the engine is hot.

Valvetrain noise is mostly gone, like 70% gone. Dead plugs = valvetrain like noise?

Cheers,

Derek

[miamibob]

Firstly, Autolite plugs SUCK. Would have asked for Motorcrafts. Secondly, it could be a bad IAC or possibly just a good TB and IAC/port clean out is required. I am certain others here will jump in with opinions....Bobby

[85crownHPP]

Yeah, I'd guess that with all the new tune-up stuff (especially if the old stuff was pretty bad) it could be just that the idle setting for the IAC is a little different and is having trouble finding it. Parts like that get a 'happy place' from working within the same range for so long, if the new range of movement includes a dirty/sticky/gummy zone in the actuator it may be overshooting its target, then pulling back over and over until it gets there. You could try cleaning it out with some throttle body spray and see if that helps.
It's also possible they disturbed a vacuum line that was already bad and opened it up a little. Try wiggling various vacuum lines (not the plastic ones though, they might break) and listen for hissing sounds or changes in idle while doing it.

Also if the old plugs and stuff were really really bad, I wouldn't doubt you had some noise that went away with the new parts.

I did a tune-up on a friends truck that had plugs more worn than I had ever seen... he called me the next day on the highway and was like "my engine seems to be running slower" ... He meant that his cruising RPM on the highway was less than it usually is, I assured him it was a good thing and his engine was just having to work less to keep him going, lol

[DerekTheGreat]

Firstly, Autolite plugs SUCK. Would have asked for Motorcrafts. Secondly, it could be a bad IAC or possibly just a good TB and IAC/port clean out is required. I am certain others here will jump in with opinions....Bobby

And here I thought Autolite=Motorcraft... Ash has 'em on her TC and things are going ok so far but I sure wish I knew this ahead of time, I would've bought & handed over plugs meself.

Yeah, I'd guess that with all the new tune-up stuff (especially if the old stuff was pretty bad) it could be just that the idle setting for the IAC is a little different and is having trouble finding it. Parts like that get a 'happy place' from working within the same range for so long, if the new range of movement includes a dirty/sticky/gummy zone in the actuator it may be overshooting its target, then pulling back over and over until it gets there. You could try cleaning it out with some throttle body spray and see if that helps.
It's also possible they disturbed a vacuum line that was already bad and opened it up a little. Try wiggling various vacuum lines (not the plastic ones though, they might break) and listen for hissing sounds or changes in idle while doing it.

Also if the old plugs and stuff were really really bad, I wouldn't doubt you had some noise that went away with the new parts.

I did a tune-up on a friends truck that had plugs more worn than I had ever seen... he called me the next day on the highway and was like "my engine seems to be running slower" ... He meant that his cruising RPM on the highway was less than it usually is, I assured him it was a good thing and his engine was just having to work less to keep him going, lol

The old plugs & wires had to be the originals. They said Motorcraft on 'em and the coil wire clipped onto the coil, can't get 'em like that anymore right? Plus when I had issues the coil was swapped to Ashley's TC and I noticed all kinds of white powder on the coil's post & the wire's socket. Surprised it ran actually.

Thanks for the tips! I'll look into the dirty IAC valve & try to hunt down any "visible" vacuum leaks, the rubbery stuff underhood does look to be pretty brittle. Some of it goes where the eye cannot see too.

[miamibob]

Autolite has not been owned by Ford (Ford only bought "part" of the company) since approximately 1973. They were then sold out to Bendix and I think a New Zealand company owns them now. Not even certain where they are made now (China/Mexico??) but MANY folks have had problems with them. I would check out the IAC, it's ports and the TB. If all else fails, swap out the plugs for Motorcraft. Just my humble opinion...

[sly]

I've had 3 motorcraft plugs of the 8 that Scott put in my 93 blow the insulator loose and allow blow-by through the plug. so I think the motocraft aren't any better than the rest any more.

[miamibob]

I've had 3 motorcraft plugs of the 8 that Scott put in my 93 blow the insulator loose and allow blow-by through the plug. so I think the motocraft aren't any better than the rest any more.

WOW! Have had them in all three of my cars and never had an issue. Guess it could happen anytime or you got a bad batch.

[sly]

one was just a month after install... another after about a year... the last one a year after that. I'm about ready to take them all out and just put the plats that the system calls for in there.

[gadget73]

The Autolite and Motorcraft plugs were identical once upon a time. At some point, the Autolite were coming from China and Motorcraft were coming from Mexico. Sad to say when Mexican plugs are the preferred item. They probably still aren't exactly ideal, or any different now.

[miamibob]

IIRC Scotty has had some "lovely" things to say about Autolite plugs!

[DerekTheGreat]

So what plugs do you guys prefer/have had good luck with? OEMS made it 27 years & 89k miles, owners manual replacement guidelines be damned!

[miamibob]

I use OEM's only but I am sure we will hear some good things about various aftermarket ones.

[cheaneyt]

I run motocraft double platinums

[gadget73]

I run boring old Motorshaft copper plugs. I've been real tempted to try Bosch Super plugs, but I don;t know if they make one for a 302. The Super is their copper plug, no platinum silliness. I've not had a platinum plug run worth a crap in an engine that didn't come with them from the factory. I haven't had any trouble with the Motorcraft plugs, but I like to have options in the event that I do.

[DerekTheGreat]

I think we put platinums in my brother's old 93 CV, mod motor did not like them and we went to champion coppers. Maybe that was the other way around? Been almost ten years since that was done.. I've got champion coppers in the 'bird and it's happy with them. Not sure if the MSD 6AL box, distributor & coil help with that. Why are platinum plugs silly? With all the stuff I'm [partially] knowledgeable about plugs are not one of them. My thoughts on them haven't changed much since high school "Run what you like, make sure they're gapped correctly." I'll never run the quad tips or whatever they're called again though, lol. Also, what type of plugs did ole mother Ford put in from the factory, copper?