87 350 TBI running lean

[Fleetwood]

I have a 1987 350 tbi truck that runs a little weird. When I put it back in park after driving it for a while, it shoots up to around 1600 rpm and slowly comes back down. Also just changed all the plugs and they were white. Driving around monitoring the sensors shows that the BLM and INT are high. Where do I start?

 

[Bextreme04]

I have a 1987 350 tbi truck that runs a little weird. When I put it back in park after driving it for a while, it shoots up to around 1600 rpm and slowly comes back down. Also just changed all the plugs and they were white. Driving around monitoring the sensors shows that the BLM and INT are high. Where do I start?

Vacuum leak. Check all your vacuum lines for cracks/old rubber and spray carb cleaner along the base of the TBI unit and around the intake manifold while running. Any change in RPM while spraying around a specific area shows that you have a vacuum leak in that area.

 

[gmbellew]

if you are monitoring sensors, IAC counts at 0 would definitely point to a vacuum leak.

do the IAC counts jump when you put it in park, and then come back down?

BLM and INT at 128 is "perfect." higher is adding fuel and lower is taking away fuel. BLM would have to be up near 150 to be really too lean. I think the computer may be able max out at 155 on the adding-fuel-to-reduce-lean side of things. and on the rich side it pegs at 108 and can't take away anymore fuel.

 

[Fleetwood]

It looks like the IAC is trying to keep the RPMs at 100 whether is it in drive or park. When I come to a stop in drive, the rpms stay at 1000. When it put it in park, they shoot way up because the load is off and then slowly come back down to 1000. In drive the IAC is around 75 and it goes down to the 30s in park.

 

[gmbellew]

It looks like the IAC is trying to keep the RPMs at 100 whether is it in drive or park. When I come to a stop in drive, the rpms stay at 1000. When it put it in park, they shoot way up because the load is off and then slowly come back down to 1000. In drive the IAC is around 75 and it goes down to the 30s in park.

I'd first try to reset the IAC. jumper A and B on the ALDL and turn key to on for about 45-60 sec. that will force it all the way closed and the computer will know where 0 counts is. turn key to off, remove jumper, and start it and see how it does.

if that doesn't help - are you on a stock PROM or a tuned PROM? have you tampered with the throttle stop set screw to adjust base idle?