1993 Cadillac STS ENGINE MISS

Tiny
KLEVEN
  • MEMBER
  • 1993 CADILLAC STS
  • V8
  • 2WD
  • AUTOMATIC
  • 69,840 MILES
4.6L ENGINE NOTICEABLE MISS @ IDLE MPG HAS DROPPED CONSIDERABLY. PLUGS & WIRES CHANGED ALSO INJECTOR RACK REPLACED. HELP!
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Friday, January 8th, 2010 AT 10:05 AM

4 Replies

Tiny
MATHIASO
  • MEMBER
HELLO_

Do you have engine light on?
If yes, have it scanned and get back to me with the code(s).

Thank you
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Friday, January 8th, 2010 AT 10:49 AM
Tiny
KLEVEN
  • MEMBER
No engine light on computor shows no problem
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Friday, January 8th, 2010 AT 11:11 AM
Tiny
FACTORYJACK
  • EXPERT
93 would not give you misfire codes, pre-OBDII. You say it misses at idle, does it not at higher, or does the frequency make it not as noticeable. For starters, use something insulated to pull the wires from the front plugs one at a time. If you pull one and get no change, then that is your misfiring cylinder. The rear bank is a bit harder to get to, so see if you can nail it down to front back without a lot of effort. Some other things might include checking engine vacuum, and listening to the injectors with some type of stethoscope(a long screwdriver works) for clicking. You could have a failed injector, broken valve spring. If you had a bad coil, chances are two cylinders would be affected.
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Friday, January 8th, 2010 AT 3:03 PM
Tiny
MATHIASO
  • MEMBER
Hello kleven
There number of things to check.

Check for poor connection at PCM or IAC motor. Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.

Inspect the wire harness for damage, including; proper routing, broken insulation, rub through, or broken wires.

A restricted air intake system. Check for a possible collapsed air intake duct, restricted air filter element, or foreign objects blocking the air intake system.

Check the throttle body for objects blocking the IAC passage or throttle bore, excessive deposits in the IAC passage and on the IAC pintle, and excessive deposits in the throttle bore and on the throttle plate. Check for a sticking throttle plate. Also inspect the IAC passage for deposits or objects, which will not allow the IAC pintle to fully extend.

Check for a condition that causes a vacuum leak, such as disconnected or damaged hoses, leaks at the EGR valve or EGR pipe to intake manifold, leaks at the throttle body, faulty or incorrectly installed PCV valve, leaks at the intake manifold, a brake booster hose that leaks or is disconnected, or a faulty component that uses engine vacuum to operate
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Saturday, January 9th, 2010 AT 1:54 AM

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