I have a 89 Lincoln Towncar 5.0L with 148k miles. It has idle through
mid range roughness. The Bosch platnium spark plugs have maybe 10K on them
and I recently changed the EGR valve and the EVP sensor in response to scan
codes. That cleared up the symptoms for about five days but the symptoms
slowly returned. The engine also seems to idle pretty slow and the tranny
seems to clunk when shifting. It is showing no codes at all and passes KOEO
and KOER test and cylinder balance tests as well. It has the original O2 and
MAP sensors as far as I know. At 150k miles are either of these past their
useful lives and could they be bad without throwing codes?
Any help would be most appreciated.
Definately be suspicious of the O2 sensors but as far as the slow Idle in
addition to all the other stuff that's been mentioned....don't overlook the
timing chain....had a 1978 Caddy come into a shop I was working at...second
time for car first time I looked at it...said he'd been back and another
mechanic adjusted timing after recent tune up....12 degrees retarded the
invoice said from factory.....sheesh....checked timing and found it
correct...did vacuum gauge check.....14inches at idle....pulled valve
cover...tdc'd #1 checked and deduced timing chain had jumped exactly 1
tooth...vary rare to just jump one tooth....customer verified diagnosis
after taking to full repair shop, mechanic called me to verify
diagnosis...just a thought.....
Thank for all the inputs. Definetely will check out the PCV and plug wires.
As far as the timing chain goes...I wonder if it has a chain or belt? I'd
imagine whichever it is it probably needs replacing so I'll check it out. I
just got done replacing the timing set on my 77 Suburban that has similar
mileage and it had 11 degrees of slop. What a difference the new set made!
Restored the low to midrange torque completely.
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