My F-150 is a 1999 with the V6, 4.2 Liter emgine, and has 157K miles on it.

A couple months ago(not long after it got CA. smogged) it started idling and running a little rough. Starts up O.K. though.

I cleaned the mass air flow sensor, and put on a new air filter. I "thought" it improved a bit. But, the problem is actually getting worse, a couple times I thought I heard it backfire, while accelerating.

I'm thinking of buying an OBD II scanner, I don't know if it would tell me exactly what was wrong.

What does it sound like, to you guys? Electrical, sensors, fuel?

Any troubleshooting tips would be appreciated.

 

is your check engine light on?
any codes
you may want to search the interwebs for ford 4.2l v6 imrc

 

Yes, the "check engine" light has come on.

Edit: so maybe the IMRC? I should go ahead and buy a OBD II scanner....

 

I'm going to get a OBD II reader, thinking of this one on Amazon:




With 157,000 miles, could the problem be spark plugs and/or wires? They've never been replaced.

 

For starters you could just stop at autozone and they will read codes.....

 

+1 on Autozone, just don't take their advice on how to fix it. Report codes back here, or google them

 

If you have a laptop with bluetooth or an android phone look at a BAFX scanner. You can get a whole lot of information. Free reading at autozone is good as well but long term having a good scanner will help. Get the codes either way and let us know what they are.

 

I did buy the from Amazon, but I won't get it for a week, so while I'm on vacation, I think I'll swing by Autozone and see what happens.

 

I went to Autozone this morning, they let me use their OBDII instrument.

Got the following codes:

PO301 "misfire in cylinder 1"

PO1450 "unable to bleed up fuel tank vaccum "

The guy at AZ mentioned that if the "misfire in cylinder 1" (bad plug or wire) situation were remedied, that the 2nd code problem "might" clear.

I did feel that at 157,000 miles, a new set of plugs and wires was not a bad investment, so I bought them. Will install later, when it's cooler.

 

Sounds like a good start on the miss fire code, The tank vacuum code however isn't likely going to go away with the misfire code, but will likely clear for quite a while when the first code is erased. The evap system monitor takes the longest time of all monitors on Ford vehicles. Most likely it would be the charcoal canister being full of fuel,and not allowing the pressure to escape, or the purge valve not functioning properly.