Bumpin' Yota

Ok here's my dilemma, my truck is running astoundingly wonderful after topend rebuild.

During cold fireups she idles a bit high as she's supposed to. Once warm and in park or neutral she holds a perfect 800rpm idle.

But put her into drive, reverse, or any other "drive" gear and the rpms drop to 500rpm and in some cases down to 450rpm!

Whats going on here?

thook

Possibly a vacuum leak. You may not think it because they can affect power and idle across all temps, but I've had one that caused a high idle, but still had relatively good power. In others, I didn't notice any drops. Anyway, in your case with an auto transmission creating a vacuum load once in gear you might have a similar problem.

I know also the coolant temp sensor and TPS are connected to ECT's. However, I'm not an expert on troubleshooting related issues and how it may apply to your case. Worth checking, though. The coolant sensor and TPS, that is.

Ain't EFI a biotch?

Belize Off Road Team

Funny thing, when i turn my fan speed to off, my idle drops to 500rpm but when i put it back on to any speed it goes up to 800-1000rpm? and this only works when my A/C system is charged, if it is not charged...my truck only ever idles at 500rpm not matter what.

4x4mike

That's because of the drag put on the system when the compressor kicks on. It'll only kick on when it is charged. The engine rpms are kicked up so that it doesn't stall, this is consistant with most vehicles.

My last truck would drop in RPMs when it was put into drive. I was told it is vacuum related and that it was operating the way it was supposed to. Does you engine die? Did it do this before your rebuild?

T-1000

Mine does the exact same thing. I thought it was normal, every car I ever been in changes RPM when you put it in gear.

thook

Oh yeah, right. Now that I think about it, this is correct. The idle does drop that low normally.

Sorry, bumpin'.....I don't drive auto's much, lately.

Bumpin' Yota

Hmm ok

I remember it dropping some rpm when going into gear but never loosing 400rpm doing so, maybe I just dont remember too well...Probably from too much time spent behind the helm of an LS1!

abecedarian

Most auto's I've dealt with have the idle speed is spec'd with the trans in drive, not park or neutral, so the speed drop is compensated for.
My 89 celica also spec's idle speed in drive. Hmm....