Drautotech

i have a 1990 c4 L98
finished doing and engine rebuild
new pistons, crankshaft, bearing, camshaft etc
bored 30 thousandths over

seems be running rough at idle.
looking to try to get a tune for it.
possibly burning or getting a chip
Are hypertech street runner chips any good? have you had any luck with them?
whats the best way to tune these motors?
i was told the ecm in the L98 are hard to tune
triedd going to a tune shop and they told me they don't do L98s :/

Thanks
Danny C

Joe C

(my 2-cents, FWIW) are you sure it's the rebuild causing the rough idle? could be something as simple as a vacuum leak, weak injector, sticky egr valve, bad plug, bad plug wire, bad ground, or a number of other things. on your rebuild - everything pretty much stock - cam, timing, etc.. you didn't do anything weird () like removing the smog pump and associated plumbing? how does the car perform off idle?

if everything is pretty much a factory OE type rebuild, i'd start with the basics. fuel, ignition, timing, throw a vacuum gauge on the thing. and not get into chip burning. baby steps, and my favorite saying - check everything down to the component level - establish a baseline -

billschroeder5842

I agree with Joe C

You most likely have a vacuum leak or a TPS out of spec. Start there by putting on a vacuum gauge, verify a steady 17-22 reading. Then checking the TPS.

Pwnage1337

What cam did you select? Is it still running the "factory" tune in the ECM?

Joe C

- ...and wouldn't hurt to give the throttle body a thorough cleaning.

bjankuski

Spot on, give us the details on what you did for the rebuild, that will help us determine if it is an assembly issue or a tune issue. (parts in engine, compression, heads, cam specifications, injector size)