So I blew my engine in my 91 toyota a couple days ago and I found a 2wd 91 toyota for a donor engine. I did the swap and had to change the wiring harnesses on the engine but other than that it was an easy swap I did in one day. So now with the new engine my idle will climb to somewhere around 1400-1500rpm's than drop down to 500 and catch itself and do the cycle again. It's also sucking down a ton if gas. Anyone have any tips or sugestions that I could try? Thanks

I know an EGR stuck open will cause it to surge like that. I've seen that before where the solenoid was constantly on - messed up ECM. Just an idea.

99.9% you have a sticking / mis-adjusted TPS.

I know an EGR stuck open will cause it to surge like that.

When my EGR was clogged it surged like you described.

Turn your idle speed down, you are hitting the ECU's fuel cut RPM:
http://www.4crawler.com/4x4/TLCA_TruckTech/TruckTech.04.09.html
And check the TPS as noted above: http://www.4crawler.com/4x4/CheapTricks/TPS/index.shtml

allright cool. I think I'll switch the EGR valve and then adjust the TPS and see if that makes a difference. Thanks a lot guys I'll let you know how it turns out