I bought a 2001 E150 4.2 litre to use as a work van. I test drove it and everything seemed to run fine at the time. When I test drove it there was NO check engine light on. Now (2 days later) it's wanting to cut off at stoplights, signs, and just at idle, when this happens I have to hold my foot on the gas to keep it from idling rough. It runs better when you are driving at speeds. Now when I think about the test drive, I drove down the interstate at speeds and only had to stop a 2 lights briefly. The rough idle didn't really have time to happen as it takes a minute or two to happen.
I put my vacuum gauge on it and it held between 17-21 for a few minutes then when the rough idle happened it dropped to 15. The needle on the vacuum gauge was erratic when the rough idle started then held at 15 on the vacuum gauge.

I bought a code reader and found the check engine light to be disconnected.
There are 5 codes showing.
LEAN CODES
P0171
P0174

MISFIRE CODES
P0301
P0303
P0305

Would the misfire cause the lean codes? Should I start with diagnosing the misfire codes first?
I did notice the guy had replaced the coil pack, plugs and wires and a new MAF sensor. This shows he was trying to fix the misfire codes. Since all this has already been replaced would my next step be the EGR Valve?

 

Welcome to the site..

Have you checked it for vacuum leaks? Codes should be addressed in the order their stored..

My first thought if the CEL was disable after repairs, was you may have been taken advantage of.
Have you contacted the previous owner to see if they will offer some help? Disabling the CEL (illegal) may have been removing a nuisance lamp 'at the time' during ownership, but if done to deceive, the ***** in your court. Are you bound by state emission testing?

 

Yes, I did contact the seller and he claims he had no idea of the check engine light being disabled OR the codes. This is odd because the parts he had replaced are the first steps to diagnosing the misfire. I am betting it started to get really expensive for him and the codes remain. I admit, I got scammed.

No. North Carolina no longer does emission tests. So there would have been no reason for them to check codes. This is why I am 100% certain he knew about the codes based on the particular parts he replaced. He also said, when I confronted him after purchase, he tried to have the van inspected but it failed. This means there was a safety issue and he never once mentioned it at the time of purchase.