I was having a misfire that was attributed to a bad ignition coil. I replaced the coil, which required removal of the upper intake (and all the fun that goes with that). While removing the intake, I accidentally broke the plastic fitting on the passenger's side of the intake that connects the RH rocker cover crankcase ventilation hose to the intake. Luckily, I had a spare intake from another motor, complete with throttle body, IACV, etc. I installed that intake, got everything hooked back up, and then started the Disco. Now to the problem....at first start, the idle is erratic and bounces from 2,000 rpm to 500 rpm. It will usually settle down to either a normal 750 rpm idle, or a slightly higher than normal idle around 900 rpm. This generates P0101 (mass or volume air flow circuit range/performance problem) and P0505 (Idle control system malfunction, blocked IACV) codes. During normal driving conditions, the high idle causes slightly rough transmission downshifts and increased braking effort. Prior to this work, the idle quality was great.

I've swapped the spare throttle position sensor and IACV onto this intake, but that doesn't change anything. I've checked all vacuum connections, throttle cable, etc., and can't find anything amiss.

Any suggestions on how to troubleshoot this and get my idle back to normal? Typical for me, I fix one problem (the original misfire) and create another!

Thanks.

 

Any thoughts appreciated before I give up and pay an expert.

 

I've had to remove and replace my intake about 8 times for various problems...

I would be tempted to swap your old intake back on since you know your throttle body, etc. is functional. That plastic fitting (the black one, on passenger side of intake, toward rear... close to front one with red ring in the middle... just making sure we are talking about the same one) screws out easily. Also, there is a replacement in brass at most hardware stores (got mine at Home Depot maybe 2 months ago) can just be swapped. I'm not sure what hoses you re-used or are from the intake you swapped in, but you might blow air through them to be sure there is no obstruction. I sprayed brake cleaner in mine (off the truck).

I had similar problems once and it was was a simple fix: I didn't get the connectors on very well... the one just behind the throttle body, the one just behind it, and the one on the cannister on the top/rear of the upper intake (I can't remember the name of it). Also, I boogered my intake gasket (the egg crate one, between the upper and lower intake) one time, and that affected idle greatly, so if you take the upper intake off you might check that. If it gets bent I don't think flattening it works (I had to get a new one for about 20 bucks after flattening failed). Did the intake sit flat when you tightened it? It is easy to get wires under it and if the connectors I mentioned are tight, you might check to see that the associated wiring (which exits the front of the intake, from the injector area) moves freely.

All of which is to say I think you either have a connection loose or you have a vacuum leak either at the gasket or one of the hoses on top of the intake.

Best,

Charlie V

 

Any chance the connectors got swapped? I think someone posted once that the IACV and coil used the same type of connector, only different colors.

 

Charlie, thanks for the tips. I'll double check (triple check at this point) all the electrical and hose connections....but I'm 99% sure they're all fine. I may also try the cigar smoke test to see if there is an obvious leak anywhere.

jafir, I'll double check, but I seriously doubt the truck would even run if those two were swapped. But who knows, it is a Disco afterall.