My son has an 87 F150 4x4, 4 speed, with the 300 6 cylinder motor. Engine idles at 2000 when started and stays idling at that rpm till you shut it off. Is this really bad and what can be done to turn it down? Also at 3000 rpm there is a knock, could this be a bearing?
I'm trying to get more information for him since he lives a couple hours away from me and he had a mechanic tell him that idling at that rpm wont cause any problems, he was in need of a vehicle so he bought this truck after the guy told him that it runs good. Of course after he paid and had the title done they guy said there was a problem with one of the spark plugs and was concerned about it running right since he had to drive it 35 miles back to his house.

 

Start by warming the engine to norm. op. temp. Then shut off the engine & disconnect the battery for 5+ minutes (not much more,you want it to pretty much remain at norm.op.temp.). Then reconnect the battery, restart and observe idle. If that didn't do it, with someone w/ their foot on the accellerator, disconnect the IAC. The idle will falter & try to stall (If it dosen't, your IAC is bad). The person on the accelerator should catch the idle & maintain it at 675(+/-)rpm. It will fight for 30-60 seconds but will settle in after that. Maintain for a minimum of 2 minutes. Then shut it off, reconnect the IAC & after 1 minute, restart. You should be looking at 675 rpm. If you have 675rpm, Turn on Lights, A/C, whatever you have that creates an engine load, and let idle for 2 minutes, then shut off for 1 minute. Re-rangeing the IAC is many times required after base timing is advances more than 2 degrees at a time. This assumes no Vac system leaks, a solid ignition system & no active error codes. I would start by removal, cleaning & re-installation of the IAC to start with. I'd also do the Seafoam treatment, change the oil & add a quart of Lucas Oil Stabilizer. Run the Seafoam in the oil for a week before changeing. The purpose is to help increase oil flow & desludge the engine. Don't get what drains out of the pan on you, it's going to be VERY NASTY! Your son's "Mechanic" is a "Moron"! Just because he can't fix something, doesn't mean it's not broke! Anytime my truck is doing 2000 rpm, I'm well above the speed limit! There's a crap load of reason's a 2000 rpm idle is detrimental. Gas eating, Clutch wearing, and not particularly that safe on slick/icy road conditions (although a seasoned driver could probability adapt, but why would you want to) .