rough running while cold

[mountaingoatgruff]

i've been driving the illegal injected hatch (its not my fault those idiots can't pass a budget) while working on the wife's legacy and noticed that it runs like poo in the morning when i'm going home from a graveyard shift (that's as close to cold as it gets here right now, unfortunately).

 

it doesn't necessarily start harder but it goes to an idle of 2000-2200rpm's until i blip the pedal then it comes down to about 1800 or so.

 

if i don't try to drive it it'll idle okay and come down just fine to somewhere around 700-750rpm's.

 

if i try to drive it though it sputters like elmer fudd after a hard night of toking and yodeling....

 

the hatch runs like a dream once it's warmed up, but not before that. more power than i'd have ever hoped for and purrs like a kitty at stoplights. i've abused this ailing 4speed a couple times lighting up the tires for folks who get a kick out of this little old rig and you should see the looks i've gotten! that's all in the 3.90's and the weight not the hp, but they don't know that...

 

replacing the o2 sensor with an oem and the y-pipe with that maremont aftermarket really quieted the exhaust down (which sucks of course) but seems to have helped it run better, especially at freeway speeds. kinda rattles since it's strung up with galvanized electric fence wire until the 5speed's in but i can live with that for now.

 

so, anyone else with an spfi or pertinant knowledge have any ideas on this one? i'm leaning toward an elusive vac leak (i've searched high and low multiple times now, where could a vac leak occur while cold and go away once warm?) or maybe a bad signal somewhere... it'd be great if i could swap out a cts or something to fix this.

[McDave]

It sounds like the coolant sensor is working right since it idles up when cold and returns to normal after awhile.

 

I would suspect fuel flow. Possibly a gummed up injector. A bottle of Techron in the gas tank sure helped my SPFI run better.

 

Past that I would check the fuel pressure, particularly since this is a SPFI conversion. It should be 20-24psi measured at the fuel inlet on the throttle body, at idle.

 

Then pinch off the fuel return line near the TB for a couple seconds to see if the pressure will reach 38-50lbs, also at idle. Don't leave the return line pinched for more than a few seconds.

 

Also check for fuel volume while you have the hose disconnected. Have someone crank it over while you watch a coffee can fill up, or connect your green test connectors and watch the pump pulse the fuel out.

 

Also scan the ecu for codes.