Thread: Hesitation at start, lean code?

Was having issues with a bad Mass Air Flow sensor. Put in a new one, and man it's workin like a charm. Two days I've put about 40-50 miles on the car and not a single issue(they were happening after about 25 miles before). However today it started having a minor issue at start. It begins to start then dies, but if I rev it for a second it starts just fine. Had this issue before and it was the battery but this time it is also giving me a P0171 code saying it's running lean. Any ideas?

I haven't cleaned it since owning the car, so at least 9k miles or so. Not sure about the previous owner.

Also, not sure if it will affect responses, but I am talking about my 2003 GT, not my 04 in my "about me" section.

Could it just be the new sensor needing a re-learn? Put a cold air intake right after the old sensor broke so never really got to learn. A vacuum leak or dirty tb just seems so random to have happened the day after I replaced the MAF sensor. How would I go about checking that.(vacuum line)

Still no opinions? Fuel filter? Pump? Vac lines? I checked all connections from intake to throttle body and everything is secure. Reset computers by disconnecting battery for 30 minutes with no success. Seems to have only made it worse, or maybe it's just naturally getting worse.

How did you check the vacumm connections? I'd grab a can of carb cleaner, fire the car up and spray around all the vac line connections, the UIM/LIM, TB, back of UIM where booster line connects and anywhere else vacuum could be leaking/present. If you find a spot that causes the engine to change tone or stumble then that is a leak. Also, check to be sure that you have 2 o-rings on the PCV valve- one around the valve itself, and the other in the lip of the UIM where the MAP screws down onto it. If one is missing it will cause a vac leak.

I'm worried it may be something more serious like an intake manifold gasket leak. Car smells like burnt antifreeze when it's acting up and looks like it's leaking just a small amount of something right under the engine bay(was sitting outside in the driveway all night so couldn't really tell what it was). Is carb cleaner safe to use because I've heard several people say they have seen first hand cars igniting with the cleaner and causing an engine fire.

Could be. Have the LIM gaskets ever been changed? Also, the plastic UIM have been known to crack and cause issues. I had one crack around one of the bolts and cause a slight leak. It still ran, but the leak was obvious in the way it ran.

You could use brake cleaner but its a bit more harsh on paint if you overspray. As long as you aren't soaking the motor in carb cleaner or spraying the exhaust mani's directly you should be fine. Might be best to do it when the motor is cold at first startup. Just a small spray here and there will be all you need. No need to empty the can, lol... Oh, and might want to wear safety glasses just in case it hits something and comes back at you. Life lesson you don't need to have.

As far as I can remember from the previous owner(10k miles ago) it has not been replaced. I will check the paperwork they gave me later tonight. I can get it to run for the most part, just have to give it some gas to get it to start or else it stalls and if you try to go above 4k RPM or so it is VERY clearly bogged down and almost feels like it's going to stall. Will get some carb cleaner and a cheap pair of safety glasses and check it tomorrow after work(while it's cold, will take the '04 to work). Thank you for giving me such useful information.

Vacuum lines seem to be fine upon visual inspection. I've got two theories from doing research I'd like your opinion on. New MAF from Standard Motor Products not being completely compatible, but I'm doubting this because it's not throwing any codes for the MAF. Or a bad EGR Valve? Not sure how you test that though. Some symptoms that may help be more specific. When it acts worse it seems to be minorly dimming the lights after idle revs. There is what looks like something leaking onto the engine on the driver side, below the intake and EGR closer to the driver than the front bumper. There is also something leaving a very small drip where I leave the car overnight. Any opinions?

Don't want to jinx myself which always seems to happen but maybe a bad tank of fuel? Was running low so put 5.5 gallons of gas from Quick Trip instead of Caseys(I normally use QT) this time. Burned through another 20 miles. Now it's starting up every time without me having to rev it(six times in a row instead of one), idle is smoother, don't see the powerloss I had before(at least not as bad), but the biggest thing really was the starting up. It would crank over for a second with dim lights then just die. Not doing that anymore.

Could have been. Might have been some junk in the last fill up. Next time you get low maybe shove a bottle of Seafoam in the tank first, then fill it up at QT.

That's what I was thinking. Seems to be running much better. Has started every time on it's own. Will probably seafoam it next week. Hasn't been done in a year. I think I still have some issues. EGR valve seems to be getting stuck every now and then but not causing major issues. Random long shifts. But nothing that's really affecting daily driving which is what I need the car for. I appreciate the feedback guys. Thank you.