This is my son's 1995 Lincoln TC signature 4.6L ~110k miles.
He lives in Michigan, a good ways from here so I got to work on it over Thanksgiving and will see it again at Christmas. I need ideas. I've read as much of the relevant info I can find on this site but we're still stuck.
He's had this problem since the weather turned cold but said he first noticed it last winter.
Symptoms
No codes. No CEL.
Turns over and catches just fine but won't hold an idle at cold start up, have to rev it just a bit then hold the pedal down slightly to keep it from stalling.
The idle stays quite low with a strong surging pattern while working through that cold start.
After ~3 minutes of idle, once the engine is warm, it idles fine on it's own.
On very cold days (<30F) it becomes noticeably harder to maintain an idle at cold start up.
On warmer days (>60F) it will almost idle okay at cold start up.
He says the thing drives fine once the engine warms up, but thinks there is a slight surging at idle at all times.
work done at Thanksgiving:
checked all vacuum lines with stethoscope and carb cleaner
reset the PCM (disconnect ground)
fuel and air filter
PCV with complete lines
cleaned MAF
removed throttlebody and cleaned
cleaned EGR channels
replaced IAC valve
changes observed after that work:
started much better, almost perfect for a few days when it was 20F but on the 4th day, even though it was a warmer 40F, it went back to the same old symptoms and has stayed there.
Maybe something is sending a faulty signal to the IAC that closes the valve even when the engine is cold?
I'm going to have him reset the PCM again and see if there's any change. I'll post the results.
Who knows? Any ideas?
parts ordered for Christmas work:
Temp sender/sensor
new Motorcraft wires and copper plugs .54 gap
will check the TPS setting with a voltmeter
He lives in Michigan, a good ways from here so I got to work on it over Thanksgiving and will see it again at Christmas. I need ideas. I've read as much of the relevant info I can find on this site but we're still stuck.
He's had this problem since the weather turned cold but said he first noticed it last winter.
Symptoms
No codes. No CEL.
Turns over and catches just fine but won't hold an idle at cold start up, have to rev it just a bit then hold the pedal down slightly to keep it from stalling.
The idle stays quite low with a strong surging pattern while working through that cold start.
After ~3 minutes of idle, once the engine is warm, it idles fine on it's own.
On very cold days (<30F) it becomes noticeably harder to maintain an idle at cold start up.
On warmer days (>60F) it will almost idle okay at cold start up.
He says the thing drives fine once the engine warms up, but thinks there is a slight surging at idle at all times.
work done at Thanksgiving:
checked all vacuum lines with stethoscope and carb cleaner
reset the PCM (disconnect ground)
fuel and air filter
PCV with complete lines
cleaned MAF
removed throttlebody and cleaned
cleaned EGR channels
replaced IAC valve
changes observed after that work:
started much better, almost perfect for a few days when it was 20F but on the 4th day, even though it was a warmer 40F, it went back to the same old symptoms and has stayed there.
Maybe something is sending a faulty signal to the IAC that closes the valve even when the engine is cold?
I'm going to have him reset the PCM again and see if there's any change. I'll post the results.
Who knows? Any ideas?
parts ordered for Christmas work:
Temp sender/sensor
new Motorcraft wires and copper plugs .54 gap
will check the TPS setting with a voltmeter
