1987 Mercury Topaz Low Idle/Rough Idle

Tiny
MIAMIBOB1
  • MEMBER
  • 1987 MERCURY TOPAZ
  • 2.3L
  • 4 CYL
  • FWD
  • AUTOMATIC
  • 165,000 MILES
I have had this problem for the past 3 or 4 years! If the dash tach is to be believed, it idles at approx. 500-550 rpm (which is low). The idle is rough and sometimes feels like it will stall (but usually does not). I have replaced the plugs, wires, car, rotor, distributor, TFI, MAP sensor, fuel filter along with just about every sensor and vacuum line I could find. Also replaced the main computer and fuel/computer relays. I had all these parts in stock and did the work myself so I though why not? The strange thing is when going from a stop light/sign, the car picks up immediately and has great power (for a small 4 cyl). Except at idle, it runs like a new car! By the way, also replaced the IAC, TPS and the one injector it has. All Motorcraft parts. Have not run a fuel pressure or compression test because of how well it runs outside of idle. Thoughts? Thanks. Bobby.
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Saturday, December 12th, 2015 AT 12:34 PM

4 Replies

Tiny
HMAC300
  • EXPERT
Clean throttle plate on both sides and iac hole with choke cleaner if it continues check fuel pressure with a gauge auto parts rent it.
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Saturday, December 12th, 2015 AT 1:41 PM
Tiny
MIAMIBOB1
  • MEMBER
Thanks for the REALLY quick response! Forgot to mention I completely cleaned out the TB, TB plate and holes. Guess I have to do a fuel pressure test (the fuel line does NOT have a valve so will have to "T" in at the fuel filter). Strange, though, it runs great other than idle. I would think if there a fuel pressure issue, that would not be the case? Bobby
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Saturday, December 12th, 2015 AT 1:48 PM
Tiny
HMAC300
  • EXPERT
Hard telling with these cars today. Check compression too if you have a 20% variance you have a problem there. Also check vacuum at intake at idle if 15" or below suspect a clogged converter/exhaust
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Saturday, December 12th, 2015 AT 2:15 PM
Tiny
MIAMIBOB1
  • MEMBER
Will have to do a compression test as well - wet and dry, if needed. There is no longer a cat convertor - just a straight through pipe so at least we know that's not an issue.
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Saturday, December 12th, 2015 AT 7:15 PM

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