The Dakota project my brother started is nearly complete. Fast recap, he has a 1989 Dakota convertible and is putting in a 318 Magnum and auto trans from a 1994 Dakota. It starts and idles fine, but after 30 seconds or so the engine suddenly races to 2000 rpms and then hunts from 1500-2000 rpm. Can't find a vacuum leak, everything is plugged in, no check engine light (other than bulb check). Truck has not gotten off the jack stands yet. Engine ran fine in the donor truck. Of course I'm 750 miles away and trying to help over the phone. No scanner available to check anything.
Ideas?
idle air control? Check connections, clean it... on or near the TB.
Is there a leak at the TB? Gasket?
Cap off the PCV and breather and see how much crankcase vacuum you're getting. The 5.2/5.9 Magnum engines were bad to suck in a gasket in the intake manifold (not the intake gasket, but a plate in the bottom of the plenum) which would result in a horrendous vacuum leak to the crankcase.
The intake gasket was replaced during the swap.
Vigo
UltimaDork
7/21/17 12:14 a.m.
Start truck and unplug the idle control motor before it idles up. If it never does idle up with the IAC unplugged then at least you know its a computer/control issue. The actual time involved probably has something to do with going closed loop and responding to a bad sensor signal that was being ignored in open loop.
What knurled said. Remove the oil cap with the engine running and see if it tries to suck you in.
Fixed. He left a big plug out of the back of the intake. I told him to check for that stuff first....
Vigo
UltimaDork
7/21/17 11:47 p.m.
Well, i'm surprised it took 30 seconds to run like E36 M3 then, but glad it's fixed!
Really cool project, btw. Got pics?
Vigo wrote:
Well, i'm surprised it took 30 seconds to run like E36 M3 then, but glad it's fixed!
Really cool project, btw. Got pics?
When it was first started it probably needed enough throttle that the leak wasn't an issue, just led to the IAC being closed further than normal. As it settled to idle and the computer reduced throttle, then the leak probably became apparent as it couldn't throttle down far enough.
