1993 Mercury Topaz runs bad when cold and intermittently wh

Tiny
STEVENX40
  • MEMBER
  • 1993 MERCURY TOPAZ
  • 4 CYL
  • FWD
  • AUTOMATIC
  • 78,000 MILES
When car is cold ( I live in NY ) it starts right up all the time and runs smooth but cannot drive it for ten minutes, even in park if you step on the gas pedal it cannot rev up if in gear it has no power it wont stall but you go very slow. Once car has warmed up it runs fine but then I will be driving at 60 and it drops down to 30 I pull over and shut it off for 2 minutes then start again and away I go. The high speed problem ocurs once or twice a day in a 15 mile run somtimes not at all. Ive checked fuel pressure and it is 50 psi. I left gauge connected and watched while I drove around block when cold same symtoms pressure stayed steady. I replaced fuel filter ignition coil, plugs, wires, cap & rotor. I checked throtle position sensor with ohm meter and its smooth and steady.I have no codes or check engine light I think it may be the mass air flow sensor even though I have taped on it with no change in idle run
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Tuesday, March 3rd, 2009 AT 6:54 PM

6 Replies

Tiny
JAMES W.
  • MEMBER
First of all, I thank you for your detailed description of your symtoms and the components you have checked. I wish others were as complete. It would save a lot of dialog back and forth. Anyway, on to your problem. If your system had a crankshaft position sensor, I would say to change it, but it doesn't. From your description it sounds like a lean condition when the engine is cold and also causing the power loss when cruising. You've pretty much ruled out a fuel loss, so my next culprit would be the intake air temp sensor. All of these I've ever seen go bad I can count one hand. But, if the IAC is telling the ECM the air is warmer than it is, it's going to send a lean mixture and this signal could be intermitent. I live in Minnesota, so I'm quite familiar with cold weather problems. We can test this theory if you can plug in a mobile diagnostic unit of a type and watch what air input #s are versus what actual air temp really is. Let me know what your thoughts are on this.
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Wednesday, March 4th, 2009 AT 11:21 PM
Tiny
STEVENX40
  • MEMBER
James, Is the intake air temp sensor used in the cold start as in open loop. I thought all parameters were fixed by the ECM until it warmed up and went to a closed loop. Steve
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Friday, March 6th, 2009 AT 3:24 PM
Tiny
JAMES W.
  • MEMBER
Even in open loop, the ECM uses information from the IAC and the coolant temp sensor (CTS). Which brings me to a question. When you first start the car, does the engine rpms go up on fast idle until it warms up, or does it stay at low idle? Also, tapping on the mass air will usually show a problem on a GM unit, but necessarily on a Ford. Let me know on the idle. In the interum, I'm going to check a couple of other sources. It's been a busy day.
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Friday, March 6th, 2009 AT 8:17 PM
Tiny
STEVENX40
  • MEMBER
James,
On start up its on fast idle and then slows down as it warms up.
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Sunday, March 8th, 2009 AT 5:24 AM
Tiny
JAMES W.
  • MEMBER
Well, from your description, it's one of two things. If you had a "crankshaft position sensor" (CPS), I would say that was your problem. But, you don't. Without any ECM codes we can only make an educated guess.
Mass air: If this were not sending input to the ECM until it goes into closed loop or was intermitent, this could cause the problems you're having. BUT, the ECM should pick this up and register a trouble code.
ECM: I'm not one to jump in and condemn the computer first off. But it looks the ECM isn't accepting fuel control inputs until it goes into closed loop and then intermitently drops back into open loop. When you pull over and shut the car off for a few minuets, the ECM resets and away you go again. The choice is yours. Personally, I'd look at the computer. Let me know
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Sunday, March 8th, 2009 AT 6:19 PM
Tiny
FOX
  • MEMBER
I have had the same problem I changed distributor, coil, fuel filter, spark plugs.

Ran better but still had the same problem.
I took the (MAS) mass air flow sensor off drove car ran alot better.

So what I think your problem is is the mass air flow sensor I will be changing mine soon around $90.00.
unless you ebay it or junk yard thing.


http://www.2carpros.com/forum/automotive_pictures/390795_sm_1.jpg

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Saturday, August 1st, 2009 AT 8:38 PM

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