87 f150 with a straight 6, manual tranny. When I start my truck there is a load knocking that only last about 5 seconds then goes away. Oil pump maybe? Not sure what it is. Also sometimes when I start it the idle goes up and down until its warmed up and sometimes it drops so low it dies but when I start it back up its fine. Any ideas or suggestions greatly appreciated.

 

Replace the oil filter! Use a Motorcraft! Best anit-drainback valve IMO. Had the same issue with my I6 and the Fram oil filter was allowing the oil to drain out of the filter resulting in dry starts. Same problem on my 5.0 and again, the Motorcraft fixed the problem. If my trucks were parked for more than a few hours, the engines would dry start. I can let either truck sit for a week now with no dry starts. Watch your oil pressure gauge and you'll see the oil pressure sit on zero while the noise is present and then when pressure builds, the noise goes away. Sure sign of a failed anti-drainback valve in the filter.

Can't help on the idle problem....sorry!

 

Your the 2nd person on here with the idle problem. It may be your o2 sensor. Because its actual term is HEGO. The computer calculates the idle based on the heat from the exhaust gases. Run codes on it to double check. Also check Ur idle air control valve and throttle position sensor.

 

My truck knocks on startup for a couple seconds after sitting overnight. It has a motorcraft filter on it...

 

Guess it could be the oil pump. The motorcraft fixed both my trucks like I said. Good Luck.

 

I'd say it's just lifter rattle till it gets oil press...might want to check the valve adjustment. Wouldn't hurt to put a mechanical oil gauge on and see what it's doing for sure.

 

I agree about the oil filter. I've also had good success with a Pure One filter stopping the startup rattle because the adbv is softer, which allows oil to flow better and seems to do a good job holding oil as well.

 

Thanks guys. Ill change the oil filter out... see what happens. And ill look into the o2 sensor as well.

 

Make sure to check o2 sensor IACV and throttle position sensor..