Rough Idle 4.0 (Cold) What next?
Thread Starter
|
Junior User
Joined: Nov 2003
Posts: 95
Likes: 0
Rough Idle 4.0 (Cold) What next?
99 Ford Explorer, 4.0 engine. 99K miles.
Had code for "random multiple misfires". Replaced plugs with OEM, replaced plug wires, installed new coil pack. No more "check engine" light. No codes stored. A recent tune-up included new fuel filter, air cleaner, and PCV valve.
What next? It still idles really rough for a couple minutes at start-up, then smooths out and runs perfectly. Re-starts with hot engine are smooth. Only complaint is the really rough idle for a couple minutes at cold start-up.
I've searched high and low for vacuum leaks or loose connections and found nothing.
Any thoughts? Stuck EGR valve? Something I'm missing?
Had code for "random multiple misfires". Replaced plugs with OEM, replaced plug wires, installed new coil pack. No more "check engine" light. No codes stored. A recent tune-up included new fuel filter, air cleaner, and PCV valve.
What next? It still idles really rough for a couple minutes at start-up, then smooths out and runs perfectly. Re-starts with hot engine are smooth. Only complaint is the really rough idle for a couple minutes at cold start-up.
I've searched high and low for vacuum leaks or loose connections and found nothing.
Any thoughts? Stuck EGR valve? Something I'm missing?
Postmaster
Joined: May 2004
Posts: 2,854
Likes: 0
Cold temp sensor....it's job is to tell the computer what temp the engine is at so the computer can make the fuel mixture more rich during cold startup, just like the old mechanical choke used to do. I suspect your sensor is not far enough gone to set a code, but that plus perhaps another weakness like IAC motor, MAF sensor, or just a dirty throttle plate causes it to run rough. Do you clean the throttle plate at least twice a year?
Postmaster
Joined: May 2004
Posts: 2,854
Likes: 0
Cold temp sensor....it's job is to tell the computer what temp the engine is at so the computer can make the fuel mixture more rich during cold startup, just like the old mechanical choke used to do. I suspect your sensor is not far enough gone to set a code, but that plus perhaps another weakness like IAC motor, MAF sensor, or just a dirty throttle plate causes it to run rough. Do you clean the throttle plate at least twice a year?
Thread Starter
|
Junior User
Joined: Nov 2003
Posts: 95
Likes: 0
OEM IAC motor went bad and was replaced about 6 months ago.
I recently cleaned the MAF sensor.
I clean the throttle plate more often than twice a year. I make it a routine part of preventative maintenance and clean it when I change the oil/filter. Every three months or every 3,000 miles. (I guess I'm rather aggressive when it comes to preventative maintenance.)
Where is the cold temp sensor? How do I check it?
Any suggestions to remedy my cold start rough idle will be highly appreciated. (It's my wife's vehicle...)
Tom
I recently cleaned the MAF sensor.
I clean the throttle plate more often than twice a year. I make it a routine part of preventative maintenance and clean it when I change the oil/filter. Every three months or every 3,000 miles. (I guess I'm rather aggressive when it comes to preventative maintenance.)
Where is the cold temp sensor? How do I check it?
Any suggestions to remedy my cold start rough idle will be highly appreciated. (It's my wife's vehicle...)
Tom
Thread Starter
|
Junior User
Joined: Nov 2003
Posts: 95
Likes: 0
Originally Posted by srercrcr
Cold temp sensor....it's job is to tell the computer what temp the engine is at so the computer can make the fuel mixture more rich during cold startup, just like the old mechanical choke used to do. I suspect your sensor is not far enough gone to set a code, but that plus perhaps another weakness like IAC motor, MAF sensor, or just a dirty throttle plate causes it to run rough. Do you clean the throttle plate at least twice a year?
sensor?
Or do you mean the Intake Air Temperature (IAT) sensor?
Tom
Last edited by Tom Norman; Jun 1, 2004 at 07:35 AM.
Postmaster
Joined: May 2004
Posts: 2,854
Likes: 0
No, not the coolant temp sender that goes to the gauge.
I don't think it's an ambient air temp sensor either.
I don't know where it is, but I know of it.....it senses the engine temp to lean out the fuel mixture.
I don't think it's an ambient air temp sensor either.
I don't know where it is, but I know of it.....it senses the engine temp to lean out the fuel mixture.
Freshman User
Joined: Feb 2004
Posts: 32
Likes: 0
Thats what my 98 4.0 ran like had the intake gasket orings changed fixed the cold rough idle do a search on it
Brent
Brent
Trending Topics
Senior User
Joined: Feb 2004
Posts: 253
Likes: 0
From: Marietta, GA
I had a rough idle problem on my '99 4.0 OHV, but it was much worse--had a hard time keeping it from stalling. Mine turned out to be a loose nut on the front of the intake manifold, which was causing a vacuum leak that I could not find, even though all of the symptoms indicated that it was a vacuum leak.
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
3 Best / 3 Worst Parts of Modern Ford Ownership
Brett Foote
10 Amazing Upgrades That Solve Common Ford Truck Owner Headaches
Pouria Savadkouei
Every 2026 Ford Engine Explained
Brett Foote
10 Ugly Ford Trucks That We Still Kinda Love
Joe Kucinski
10 Things Every Truck Owner NEEDS (2026 Edition)
Michael S. Palmer
Rezvani's Latest Post-Apocalyptic Monster Is a Ford F-150 Raptor Underneath
Verdad Gallardo
Top 10 Most Expensive Ford Trucks Ever Sold on Bring a Trailer
Joe Kucinski
2027 Ford Super Duty Buyer's Guide (Every Model, Engine, & Package)
Brett Foote