my car runs fine in park, when you put it in gear it stalls out. What could the problem be.

HOT or COLD...both times?

usually happens when the engine warms up. After it has running for awhile.

you DO know this could be MANY things as now is a guessing game...you could get a cheap handheld scanner stick it into your OBD-II port (not three feet from the ignition) and read what is up with your system...if it's a bad TPS...it will know...tho should have issued a CEL...some problems do not~

one not so pricey process of elimination would be to replace each and every butyl-rubber black (coaltar-and chewing gum) cracked and bloated lines with silicone ones...bout ten times more expensive, but will last forever and not crack bloat or leak and remain flexible as a silicone implant~ be methodical...replace them one at a time...summitracing offers them in various colors too~

sounds like probably maybe a Intake Air Temperature sensor...as this might make the thing run rich, black and chokey...did you witness the sight and smell of the exhaust?....was it running black?~~ https://www.google.com/#q=1999+Mercury+Grand+Marquis+air+intake+tem p+sensor

I have had it hooked up, the only thing I am told is that it could be a bad o2 sensor. Another person told me that its my coils.

see, it's tellin' the computer there is COLD air in the intake plenum...makes the combustion RICH and fouls the plugs~.....just a guess...don't call your lawyer right away~

the 02 sensor would toss up a check engine light CEL, right away...do not collect $200, coils....being individual coil packs would idle humpty- dumpty~and not have any power~.....so nay on the ignition theory~ sorry~

...and would store a trouble code with that as well....get a fifteen dollar scanner or bring it to an 0'mallory's for a free scan~

...also the 02 sensor failure would make it run POOPY and black horrible exhaust as well~

the intake air temperature sensor is situated on the intake plenum...most easy to replace....and cheeeep too~

...another consideration is the Throttle Position Sensor or tps...99,,,,WORN...these will make the throttle behave properly~ https://www.google.com/#q=1999+Mercury+Grand+Marquis+TPS

okay....thanks.~

I'm having the same issue and i have a hunch its the transponder chip in the key, she runs like a dream and then dies out and sometimes wont start up for 10 minutes, getting gas and all the coils and plugs are new, also could be dirty air sensor or cps

Its possible its the torque converter or vacuum actuator on transmission or possibly crack or broken vacuum line

WOW, I have the same model and type car and the same thing has been happening to me. Not everyday and only when its really cold. Could this be a manufacturer defect of this car?

My Mom is having the same problem with her 2002 Mercury Marquis. The car cranks but as soon as she puts it in gear, the engine goes dead. The check engine light also comes on. Happened twice last year. She is older and had to have car towed twice. Today she called me and it happened again, almost a year later. Got the car towed home. 2 hours later went out and the car cranked and went into gear and drove fine. Any help would be appreciated.

I have a 1997 Dodge Neon That is startind and then put it in drive it will die

My car (2002 grand marquis) does the same thing. When it's cold out, start it up, put it gear (drive or reverse) and it will stall. This will happen until it warms up a bit more. Also, driving down the road while it's snowing it will have misfires. I changed the I take temperature sensor and it didn't fix it. I changed the throttle position sensor as well and that didn't fix it. My next change is likely the mass airflow sensor.

I have a 1984 mercury grand marquis that does the same thing but not black smoke what should I do but at a low coast

My 2003 Ford focus does the same thing

i have a 93 chevy lumina it run fine in p,r,n when i put it in drive it stall and die what can be the problem

My 2001 Gran prix does the same thing. When i put t into gear it dies. i put a new throttle body sensor in it, cleaned out the throttle body, and checked the coils. Still does it .backed it out of the garage just fine. as soon as i put it in drive, it died. then it started fine, put it in drive, then died again. Step on the gas and it revs fine. Im thinking that the main problem is valves. When a car is idling, it runs bc the valves dont have to move as fast. but when you put it in drive or gear they do and they are sticking. So replace your valves and they will run fine.

A fast easy and cheap thing to try is a new fuel filter I had this problem of stalling in gear and had a po171 code to lean every forum I looked at called for checking sensors and for vac leaks and the entire time it was nothing but a clogged fuel filter put on a new one and it runs great.

Cold,restarted three times,the third time it started right up as fine as usual

I'm working on the same issue on my 91 chevrolet lumina euro. I've done a lot of work on it chasing a gremlin. Pulled and rebuilt wiring harnesses, replaced a cracked head, bent intake valve, snapped timing chain, replaced all vent lines (windshield wiper hose is actually excellent for small lines. Its much more flexible than the hard multi-color lines which i assume are poly.) Throttle body, intake plenum and manifold, egr gaskets, head obviously, and valve oil seals... and ofcourse everything on the serp belt paired with an ac compressor delete (ac was shot.) 02 sensor at the header, tps, that other sensor on the throttle body i forget, iacv, remanned ecm (to the early 90s chevy guy, open that ecm up and make sure your prom chip is properly seated. Its likely bright blue and its the only thing you can remove in there), torque converter following engine removal.. starter. Im getting tired here. Anyways, if i get to the bottom of this, which i will, i'll post up the answer. Thumbs up on nixing the coils from the list, throttle position sensor causes erratic running no matter the gear cuz it cant tell where idle is, vacuum can make your car run like crap if it runs, but shouldnt just kill it in drive. O2 sensor shouldnt only kill it in drive, it would constantly be sending your ecm bad information on the mixture. It seems like a tranny issue to me. Hell, if i were in your shoes id make sure there was fluid in there. Torque converter can seize im told, but I think if that happened the car wouldnt run at all since its bolted to the flex plate thats always spinning on the engines crank shaft. Im not too familiar with tranny electrical, so there may be a possibility in there. Maybe a vehicle speed sensor, "vss", dont know exactly what it does yet in terms of physical operation. Sorry for the long post, trying to get the brain firing, yours and mine. For credibility purposes, I'm a prior service tank mechanic, and no, i dont use zip tys or drugs. This cars got too much of my blood on and in it for me to let it go. I'll keep you all posted, and if you have any theories give a shout out.

I have a 2001 66 Marvel it starts up fine runs soon as I put it in gear it stalls out could it be the neutral switch

I have the same problem with my 03 mercury sable

I have the same issue with my 2013 dodge avenger

Guys try your mass air flow or map sensor...or replace both

I have the same issue with my 2005 Ford five hundred. No codes I’m thinking it’s the torque converter... hoping it’s not.