Hesitation At Lower Rpm

[tomtheslacker]

Hello all. First post, so nice to have a resource like this.

I recently got a hand-me-down 1991 LS 400 from my brother-in-law. 771K and still going (more or less...)

It had a leaking fuel line, so I replaced all 3 lines and the fuel filter. I also changed the air-filter, cleaned the TB, and changed the oil. I now have a rough running isse...

Car won't start on first attempt, but will always start on second try. It runs rough for a while after startup, but is still driveable. It will pull at WOT just fine, and it seems that all problems go away at 2500 rmp. It is as if it has a separate set of cams of something, because it will start to haul right away. It seems that at low rpm, and under heavier load like a hill, it will start to bog down and start to chug, but so long as I go to full throttle, it will overcome it.

I have cleaned the MAF, and checked the plugs (which were fine.)

The car has thrown no codes at all, so any suggestions would be appreciated.

Thanks in advance!

[steve2006]

Hi and welcome to the LOC.

771K is that miles or Kms because I think that may be a record for an LS V8!

Recheck all the vacuum pipes you removed to clean the TB there are loads of them and if one is off or leaking it may be the cause,did you remember to reconnect the MAF although normally this would throw a code and illuminate the EML.Make sure you didn't get any cleaning fluid in the TPS when you cleaned the TB.

[tomtheslacker]

BUpassed the fuel pump resistor so now she runs great. I went to a local yard but both cars they had were missing the part. Gues I will have to call the dealer. Now if I could only get it to start the first time. It starts on second try every time, but will not fire up on first attempt. Any suggestions? And that is km, so 478K miles...