New member 1993 Lightning

M

Moosehound

New member
Hello everyone, I just bought a 119k mile 1993 black Lightning and have a few questions. First the truck idles high around 1000 to 1200 rpm and has a very hard 1st to 2nd gear shift. I'm thinking vacuum leak but would like to know where to start to diag this issue. Truck runs good once the rpms are up but fells sluggish off the line.
 
welcome Phil. there's a vacuum hose diagram on the underside of the hood, check all of those hoses and connections. pcv valve grommet in the lower intake at the passenger side rear (very hard to see, have to feel). white vacuum hose on passenger side going to the hvac box is bad to crumble. egr valve diaphragm and diaphragms in the thermactotor and evp solenoids on the driver side top rear of intake manifold. hose going to fuel pressure regulator and vaccuum caps on vacuum tree at rear of upper intake also. this will be a good start. you can also check for diagnostic trouble codes in the pcm.
 
Thanks for the tips on where to start. It's great to have a good resource of knowledge from everyone here. I was looking at the forum and found lots of great info. Should I pull the IAC harness off to see if the idle changes to know if that is stuck open? I also noticed that my AC does not change much in sound when switching to MAX. Don't know if that is another symptom of vac leak.
 
I found a crack in that white vac line going to AC now I have max ac again. Still idling about 1000 to 1100 rpm. Pulling the IAC wire caused the engine to die so I am guessing it's not that. All the other lines look ok. Haven't pulled codes yet or checked pcv
 
Moosehound said:
I found a crack in that white vac line going to AC now I have max ac again. Still idling about 1000 to 1100 rpm. Pulling the IAC wire caused the engine to die so I am guessing it's not that. All the other lines look ok. Haven't pulled codes yet or checked pcv
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Nice. Keep us updated. I'm interested in seeing what's up.
 
Check throttle body plate and make sure it moves freely and closes completely. Don’t mess with the adjusting screw except as a last resort if nothing else works.
 
I did a base idle reset to get it to idle without the IAC connected at 650rpm and it held there without issue. Then I reset the TPS for .96 volts and then unplugged the battery for 20mins and reconnected the IAC. That process helped as it is now idling around 950 in park and 850 in gear. Still seems to high but much better then before. I don't understand why the IAC is adding the additional rpm if that is controlled by the CPU.
 
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