DerekTheGreat
Forum Regular
Ok, I read through all four pages and no one has touched on this but...
I owned an '88 454 TBI truck. I too, saw that the factory tach (once installed, did the '90.5 moonie to needle swap) was reading 1000 rpm's while hot at idle. I did not have my MT2500 at the time so I ran through all kinds of hoops replacing everything from the IAC to the MAP sensor to the TPS, ECT sensor and rebuilding the throttle body & setting the timing and messing with base idle. NO CHANGE. I finally got a good deal on a MT2500. Hooked it up, info said it was idling at 800, tach just indicated 1000. Then I read somewhere that these idle higher than the tree-fiddies to help protect the cam, flat tappet and such. Makes sense. I relayed this to my one buddy who asked me a simple question; "Did it sound right?" Yeah I guess.. He almost smacked me. Would've been justified. Like everyone else was saying, you need to be able to see the data. My IAC counts were never 0, which would've indicated the computer was trying to compensate for a high idle condition which also would have set the CEL. I verified this by playing with the base idle; if I lowered it, more IAC counts to compensate & vice versa.. Now, my base idle did need to be adjusted slightly higher (I suspect someone else was frustrated by the "High idle" before me, as the cover was already punched out on the TBI) as the idle would hunt on cold starts, something else I read somewhere as normal for base idle being out of spec. Food for thought man, good luck with it!
I owned an '88 454 TBI truck. I too, saw that the factory tach (once installed, did the '90.5 moonie to needle swap) was reading 1000 rpm's while hot at idle. I did not have my MT2500 at the time so I ran through all kinds of hoops replacing everything from the IAC to the MAP sensor to the TPS, ECT sensor and rebuilding the throttle body & setting the timing and messing with base idle. NO CHANGE. I finally got a good deal on a MT2500. Hooked it up, info said it was idling at 800, tach just indicated 1000. Then I read somewhere that these idle higher than the tree-fiddies to help protect the cam, flat tappet and such. Makes sense. I relayed this to my one buddy who asked me a simple question; "Did it sound right?" Yeah I guess.. He almost smacked me. Would've been justified. Like everyone else was saying, you need to be able to see the data. My IAC counts were never 0, which would've indicated the computer was trying to compensate for a high idle condition which also would have set the CEL. I verified this by playing with the base idle; if I lowered it, more IAC counts to compensate & vice versa.. Now, my base idle did need to be adjusted slightly higher (I suspect someone else was frustrated by the "High idle" before me, as the cover was already punched out on the TBI) as the idle would hunt on cold starts, something else I read somewhere as normal for base idle being out of spec. Food for thought man, good luck with it!
