[Gulfstream1]

I have a 3.8 98 windstar. Heres the scenario. I'm sitting in traffic with my foot on the brake. The cars ahead me move up a little so I let my foot off the brake and ease up a little never putting my foot on the gas. Consisently 4 seconds after letting off the brake pedal the rpm's will drop to 300-400 for about 2 seconds and sometimes it will stall, sometimes it will recover. This is very aggravating in drive-thru's. I had codes P1537 and P1538 and found the IMRC on the front of the engine is bad. I used a ty wrap to close the valve hoping this would be the culprit, but it seemed to make no difference. I also took voltage checks of my DPFE and IAC. The resistance in the IAC was a little high (.2-.3 ohms) but i have a cheap meter so that could be a tolerence thing. I also changed the PCV valve and cleaned the hoses. I don't know where to go next so I have come to see what the Windstar Genuises have to say. I appreciate any advice anyone may have.