Help! Engine loops 1990 L98

[fill]

Having trouble with my L98 surging. When engine is cold, it runs good, no surging. After running for 10 to 15 minutes [ well after engine temp has come up to normal ] it will start to surge or '' loop''. I replaced the I.A.C. last summer ( about 5000 mi. ago). The surge started about mid June this year (2009). Since then I have relaced the throttle position sensor, the E.G.R. valve, ajusted valves, checked timing, and ran some fuel injector cleaner ( Lucas ). None of these made a difference. I also would like to upgrade the throttle body. Can anyone tell me the stock size in mm? Any thoughts on a BBK 52mm throttle body? I would like bolt on with no special modifacations.

 

[vetteoz]

When does it surge; at idle or when cruising?

Stock TB is 48 ; 52mm is waste of money on stock engine, Would get better results upgrading exhaust; headers , freeflow cat , etc.

 

[fill]

It loops when cruising and idle

 

[aklim]

When you took out the IAC and replaced it, did you clean the housing and change the gasket? What about the rest of the TB?

 

[Schrade]

Vacuum leak.

Search my posts for vacuum leak diagnostics.

 

[Hib Halverson]

I'd agree with "Schrade".

First, check for vac. leaks.

 

[toptechx6]

Another common issue easy to check would be to test injector resistance with an ohmmeter.

 

[jjudy]

Possiable head gasket

You might want to pull the plugs and look to see if any of them are white or gray. This would indicate that the head gasket is leaking water into cylinder. This engine is known for this on driver side rear cylinder.