I have about 175k on my '99.
It runs great, good mpg, except the service engine soon light is on, and I get Po171 and Po174. Have to get emissions test done soon.
No vacuum leak found. here's what I've done:
New pcv elbow (at throttle body);
New plugs;
New fuel filter;
New air filter;

I have the original, untouched MAF and DPFE sensors. I'm leaning toward DPFE, any opinions? The hard starting almost makes me wonder about fuel. Would a bad dpfe cause hard starting? Will check pressure next.
Thanks.

 

Yes, test the fuel pressure.

DPFE wont throw lean codes, it will throw EGR codes.

Exhaust leaks upstream of the front O2's will also throw lean codes.

 

Ok, thanks. I do have a slight leak at the egr tube. The hard starting makes me think it's more like fuel pressure issue, maybe throw in some injector cleaner and see what happens.
Thanks again.

 

You are going to have to fix that leak at the EGR tube before the lean code on that side will go away.

I'd go to the parts store and borrow a fuel pressure gauge.

Best injector cleaner is Techron.

 

Yes, I use either Techron or Redline. I have some Techron, so I'll dump in a bottle and see what happens.
Think I've only used cleaner in this truck once or twice in 15 years. Probably really needs cleaned. But it idles and accelerated beautifully, just like it always has. I bought it new.
I also changed the fuel filter for the first time this fall.
Thanks again,
Tom