I have a 2000 f150 5.4l v8 XLT. On a cold start, it will shoot up to 2k rpm, and fall down to around 1k. Then, itll warm up and idle at 900rpm until I put it into gear. Since its idling too high, itll slam into reverse or drive, slowly destroying my transmission. Once its warmed up, it will idle properly at 750rpm, but anytime the engine is cold, it does the same thing.

If it was a vaccum leak, why does it eventually idle properly? I tried cleaning my IACV, but I'm not sure what's going on. I need to fix this issue as it's going to eventually destroy my transmission I'd imagine. Please help.

 

Dropping it in gear at 900 rpm should not damage the transmission, that's a reasonable idle speed until it's warmed up. If it's slamming, you have a transmission issue.

 

Even if it no longer happens at a lower rpm? If it idles down to 750, it shifts fine.

 

Sounds normal to me.

Most every gas vehicle (with EFI) I've used in my life, when you start it, the RPMs shoot up to about ~2,000 RPMs, then drop down to 800-900 RPMs until it gets warmed up enough, which about 2-3 minutes, depending on ambient temperature. Then it will fall between 650-800 RPMs.

Only vehicles I don't normally see this on are diesels. They will start, jump to maybe 1200-1400 RPMs, then fall right down to like 650-750 RPMs. Then if they have the logic to detect if it's cold enough out to warrant an elevated idle, it will ramp it up to maybe 1000 RPMs. Unless you have a high idle controller... but that's beyond the scope.

Like glc said, this does not hurt the transmission.

It's not like you are neutral dropping it at the rev limiter.

 

Thanks for the reply. So its likely the transmission? It's just strange that it's doing it at 900rpm but not 750. Any reccomendations on a solution? It slams down into reverse on cold starts.

 

When was the last time you changed the transmission fluid?

 

i just bought it. The previous owner says he did it at 100k, and it has 122k on it now. Fluid was low but it looked good and red. I added lucas transmission seal and hard shift fix. It helped but the first shift on a cold start always slams still. I'm just assuming it correlates with it being at 900rpm, but I could be wrong.