FORD F150 XLT LARIAT Intermittent engine stalling, surging and bucking

For the most part my truck runs fine, check engine light is on all of the time now. However, on random occasions the engine acts up seriously. we have been trying for months now to self diagnose being that the previous mechanic could not find the issue. On the occasions that it acts up, the engine will die immediately after starting. After finally starting it again the idle is erratic, going from 2000 to 100 rpms violently. I will step on the throttle to try to save the surge and there is no response. It catches and idles extremely high to almost 4000 rpms and then returns to normal idle. After this fiasco I’ll think I’m in the clear, go to drive and the truck won’t accelerate past 1000 rpms and will instead have no response. I park the truck turn it off and back on and the issue is cleared. I’m sincerely at a loss. I’ve thought of bad fuel injectors??? Tps sensor? The iAc valve was not the issue I unplugged it and same issue just lower idle. The egr and map sensor are both replaced. Also have new intake manifold gaskets on. No vacuum leaks have checked multiple times. Brand new air filter… etc. praying it’s not an electrical issue

What’s the year, and how many miles on the engine?



Unless a vacuum leak was created in the replacing unlikely.

If that was done incorrectly it could cause it. If so spraying starter spray here and there and noting if the engine speeds up would show you the a rea where the air leak was occurring.

A problem w/the iac valve would be my first guess. Second guess would be the throttle plate is sticking. Replacing the iac and cleaning the throttle plate makes sense. Sometimes just knocking the iac with a screwdriver’s plastic handle will get it working again temporarily, so that’s worth a try.

I had a problem similar to this on my corolla one time. It was caused by the IAC not properly controlling the amount of extra air allowed into the engine. To fix it I disabled the IAC completely. Works ok in my climate, the only downside is I have to keep my foot on the accel pedal to prevent stalling at stop signs when first starting out on extra cold days. In a cold climate this would be too inconvenient and I’d have to replace the throttle body as the IAC is not a separate part on this particular engine.

If your engine has the drive-by-wire technology, that’s probably where the problem is. Start the diagnosis by reading out the engine diagnostic codes and posting here, along w/model year and engine/transmission configuration.