Poor idle Mondeo problem

[SMAndy]

Hi everyone,

I've had a problem with my '96 mk2 mondeo LX 1.8 zetec for a while now, and no one has been able to fix it. I've had ford plug in a computer to it, to attempt to find the problem, but its not given me much luck.

Basically, when cold, the engine runs fine, i'd guess because of the automatic choke/ECU putting in extra fuel. When the engine gets warm, and this stops, the idle when i stop (at lights, junctions, whatever), the idle drops to around 500, hovers there for a second, then comes back up. This has caused a stall a few times, but its more annoyance than anything else, as it makes me wonder if my car is on the way out.

I've had the idle control valve replaced, tried unplugging the fuel pressure regulator, and had the fuel pressure tested. My Haynes manual for the car says fuel pressure should be around 2.1 bar +/- 0.2. It was measured at about 2.0, which is within tolerance. My mechanic said it should be at 3.3.... which is weird. I've not had any of the fuel system replaced, as these things can be quite expensive. I've also cleaned out one of the valves (EGR? one behind the exhaust manifold), and had my exhaust manifold replaced, as it was cracked (quite badly, too).

Anyone else had a similar problem, or happens to know a likely cause for this fault?

This was originally quite a bad problem, as the car would invariably stall at the bottom of the hill i live on, when cold. I had the temperature sensor and sender replaced, which has fixed this problem. Discovered the fix for that because my temperature gauge hadn't worked for ages! It does now, which is awesome.

Anyway, thanks for any help you can give, If you have any more questions that need answering before you can help, let me know. I'm not a mechanic, but i don't mind getting my hands dirty, and i've changed the cam belt myself, so I know where things go. I also have the haynes manual to help me find parts if you reference them.

Cheers,

SMAndy

[mintalkin]

this is worth a read.

http://www.btinternet.com/~madmole/Referen...#Plenum%20Leaks

[ccfc1987]

Hi everyone,

I've had a problem with my '96 mk2 mondeo LX 1.8 zetec for a while now, and no one has been able to fix it. I've had ford plug in a computer to it, to attempt to find the problem, but its not given me much luck.

Basically, when cold, the engine runs fine, i'd guess because of the automatic choke/ECU putting in extra fuel. When the engine gets warm, and this stops, the idle when i stop (at lights, junctions, whatever), the idle drops to around 500, hovers there for a second, then comes back up. This has caused a stall a few times, but its more annoyance than anything else, as it makes me wonder if my car is on the way out.

I've had the idle control valve replaced, tried unplugging the fuel pressure regulator, and had the fuel pressure tested. My Haynes manual for the car says fuel pressure should be around 2.1 bar +/- 0.2. It was measured at about 2.0, which is within tolerance. My mechanic said it should be at 3.3.... which is weird. I've not had any of the fuel system replaced, as these things can be quite expensive. I've also cleaned out one of the valves (EGR? one behind the exhaust manifold), and had my exhaust manifold replaced, as it was cracked (quite badly, too).

Anyone else had a similar problem, or happens to know a likely cause for this fault?

This was originally quite a bad problem, as the car would invariably stall at the bottom of the hill i live on, when cold. I had the temperature sensor and sender replaced, which has fixed this problem. Discovered the fix for that because my temperature gauge hadn't worked for ages! It does now, which is awesome.

Anyway, thanks for any help you can give, If you have any more questions that need answering before you can help, let me know. I'm not a mechanic, but i don't mind getting my hands dirty, and i've changed the cam belt myself, so I know where things go. I also have the haynes manual to help me find parts if you reference them.

Cheers,

SMAndy

as you have had a sensor changed you might have to reset the ecu try it and see if it makes any diffance

[SMAndy]

Thanks, but I've already reset the ecu... should've mentioned that one. Done by both resetting error codes, and by having the battery unplugged for over an hour.... No change.

Error codes read "engine running lean" which points to the lambda, which has also been replaced. Ford computers read it as fuel pump pressure low, even though it reads the same as the spec in the haynes manual.

It could also be that the running lean is making the ecu think there's low fuel pressure, i suppose. When i get some free time during daylight hours, i'll poke around and check for plenum leaks.

Thanks for the help.

[ccfc1987]

Thanks, but I've already reset the ecu... should've mentioned that one. Done by both resetting error codes, and by having the battery unplugged for over an hour.... No change.

Error codes read "engine running lean" which points to the lambda, which has also been replaced. Ford computers read it as fuel pump pressure low, even though it reads the same as the spec in the haynes manual.

It could also be that the running lean is making the ecu think there's low fuel pressure, i suppose. When i get some free time during daylight hours, i'll poke around and check for plenum leaks.

Thanks for the help.

possibility is a vacuum leak. All air entering the engine must be measured. Air Intake System Any unmeasured air entering the engine will cause a lean fuel mixture and will result in a rough idle. Check all the vacuum lines and hoses and make sure they are supple and have no cracks. Also make sure they are connected tightly. If the hoses are stiff or have little cracks in them, replace them. Also be sure that the lines are connected to the proper devices. There might be a Vaccum Hose Routing Diagram under the hood that will help you make sure the hoses are connected propery. As a Scottish Chief Engineer once said: "The more they overtake the plumbing, the easier it is to stop up the drain."

also check the air mas senor

[SMAndy]

I'm pretty sure the MAF is fine. It looks brand new even. I'll definitely give it a check over this weekend. Thanks for the suggestions guys.

[covlad1987]

I'm pretty sure the MAF is fine. It looks brand new even. I'll definitely give it a check over this weekend. Thanks for the suggestions guys.

did out find out whats up with it