what causes surging with FI

[big83chevy4x4]

working on a 94 gmc safari with the vortec 4.3l. its been sitting for about 6 months waiting for me to finish the motor swap (talk about a PITA), fire it up, time it correctly. and the idle surge, sometimes it dies when it gets too low. if you put the slightest touch on the gas petal, it stops, but idles too high. i was told a bad fuel pump, could it be the 6-9 month old gas?

 

[dhcomp]

I was going to guess fuel pressure too, but old gas could definitely do it.

 

[big83chevy4x4]

oh yea, the fuel pump is 4 years old, AC Delco.

 

[Thunder]

Bad gas, vacuume leak. dirty IAC, tps adjusted wrong, Clogged fuel filter. Lots of stuff to check before replacing the fuel pump.
Have you checked trouble codes?

 

[big83chevy4x4]

no codes, no vacuum leak, IAC is clean, tps is adjusted correctly, fuel filter... it was changed when we did the pump, probably should do it again.

i just remembered that it takes a few seconds after you let off the gas for it to return to idle.

 

[Big Red]

i bet its a combo of the bad gas and fuel filter. at advance i get a lot of poeple with the Astor/Safari vans that have that problem. though most don't let it sit for 6-9months. lol. just change the filter and i bet you'll be fine.

 

[big83chevy4x4]

ok, ill get a FF tomorrow and put it on and put some new gas in it.

if anyone has ever done a motor swap on a safari, you will know why it took my 6 months lol. its a very tight fit on everything.

 

[Ryan B.]

I have read over on thridgen.org about this problem with tpi engines...Everyone says replace the CTS.
Replace your Coolant Temp Sensor.. It's probably around $9.00 ?

Or more fuel at idle might fix the surging, like fuel psi?

Mine will surge when i first start it up sometimes... after a minute or two when it goes into closed loop its fine.
My friends tpi vette surges at idle quite a bit also pretty much all the time, but both of our engines have cams so that might be part of it.

 

[big83chevy4x4]

the coolant temp sender is new, i broke the old one off
it seems to be getting better (not doing it so much) the more it runs, maybe its just bad gas or gummed up filter.
also when driving for a while, 15 minutes or more, and stop at a light, it doesn't do it, but if it sits long enough it starts to do it.

 

[dyeager535]

Does it surge whether cold or hot?

 

[big83chevy4x4]

both, but we have never gotten it hot for very long.

 

[CyberSniper]

Usually when the MAP sensor goes bad it'll just run like **** but still run.

Is the EGR valve not closing all the way?