Ok I normally don't do this but I need expert help.

My 305 LU5 crossfire is acting up(no surprise )

Problem:Erratic idle

No codes are showing

Black smoke at times(running rich I guess ?)

Rpms good when cold but after it warms it goes down and wants and does die out.

Idle fluctuates up and down


My guesses is a throttle position sensor,Timing,Bad injector.I already did a ALL GM tune up last October T45 plugs,wires,cap,rotor,dist.


Any constructive input would be appreciated


Thanks
Dave

 

Sounds like bad injector...

 

Temp sensor.. maybe..
that'll make it run rich if it is telling the computer that it's colder then it is.

 

The throttle shaft bushings could be worn.That could cause all the problems you've listed but won't cause the SES to come on.You may want to join,if you haven't already,the Crossfire Injection Vault( http://www.crossfire.homeip.net ).There is a lot of good info,and good people as I'm learning,to be found there for the crossfire setup.Most there have '82 or '84 CFI Vettes but the same principals apply to our LU5's.

 

test the TPS. hook up a VM and move throttle. should show smooth succession of voltage readings.

look at the injecctor as it fires. should be nice conical spray no drips.

temp sensor possible as well.

i would check for codes anyway. might still have a code hiding. most auto parts stores do for free.

how old is 02 sensor? i think the scan tool will show its functionality as well.

 

Thanks guys

I think its one of the injectors.The rear one is not spraying in-sync with the front one.Acting like a clogged shower head spraying fuel everywhere.BUT it has flashed for a tps sensor before but just disappeared after time.Temp sensor ??

02 sensor is new Bosh installed with the tune up last October.

 

Replaced the throttle position sensor,But no luck I guess its time to rebuild the throttle bodies. Thank G*d its only around 100 bucks for both

 

i would check with Dan(Lions Den) at crossfire forum on the rebush.

 

Try applying/spraying a thick oil onto the exterior ends of each throttle shaft bushing (where the shaft inserts into the TBI body). If the idle fluctuation goes away for a brief period of time (while the oil prevents the vacuum leak), then it would confirm that you need the a bushing installation for each throttle shaft.

Try it first before you take the plunge.

 

I had 83 crossfire did the same thing after going over it couldn't find anything when i finally went to swap to a carbed setup and rebuild the 305 I found the IAC valve loose apparently and was sucking air, when i pulled the heads the exhaust valves were white from running so lean

 

Thanks,But Where are they located ?? I couldn't find a illustration in my '82 service manual.Or if its in there what page ??

 

The throttle shaft bushings are the circular holes that the throttle shaft rides within. I think you should be able to find the 2 locations (per throttle body) where the throttle shaft enters the TBI body.

 

You MUST check the temp sensor in the front of the manifold.
It will, and often causes the symptoms you are describing?

 

I guess it wouldn't hurt.They only cost $8-10.