01 Crown Vic, weak cold starts and a mystery issue. Not IAC. Stumped

[Gasbuggy]

This Vic has just over 100k on it and I've been driving it for about 4 months. The problem started after I began driving it. Any Crown Vic starts up with a nice rev then the idle comes down. Mine starts with the normal amount of cranking but fires up sluggishly right to low idle. BUT, if the engine is even slightly warm, it starts up normally the way it should. I sprayed carb cleaners all over checking for a vacuum leak. Internet research seemed to suggest the IAC was the problem. I put a brand new Delphi in (OEM supplier) and it did not change anything.

It seems to be in good tune but something may be wrong. I put new Motorcraft Platinums in soon after I started driving it, the original plugs looked good. My MPG is 20-24. Very solid for a P71 with 3.27 gears. It was never in service as a police car, it lived an easy life as a Chief's personal car. It does seem a little choked off to me though. On two separate occasions, the car had more power and was making more intake sucking noise and exhaust noise when you rolled into the throttle. Seemed to gain 30 horsepower. The first time was for a full trip, the second time, for about 5 minutes driving in the rain. I considered changing the fuel filter but it looks newer. I checked with my scanner to make sure the IAT sensor wasn't misreading and making the engine pull timing.

Not sure what to check next.

 

[Lubener]

Cleaning of the throttle body and a check of fuel pressure come to mind.

 

[Kestas]

I had the exact same problem with my 1991 Mercury Grand Marquis. I replaced the temperature sender, throttle position sensor, and even the engine computer. Nothing worked. I could never ever figure out that problem.

I've come to the conclusion that Ford engineering is very weak when it comes to throttle issues. I've seen other problems in other years where idle problems are unfixable.

 

[irad]

Check ground to battery wire for corrosion and ground battery terminal to starter, ohms with ignition off and volts while cranking.

 

[mk378]

The fast idle when cold is controlled by the ECT not the IAT.

Check for air leaks anywhere after the MAF sensor.

 

[WyrTwister]

If it has a vacuum brake booster , Check for leaks in that area , including the hose .

Check the sensors to see if all the wires / vacuum hoses are plugged in OK .

Did you check at the gasket between the head & intake manifold ? Between TB & intake ?

What year model & miles ? Which engine ?

 

[Dave9]

Check battery voltage, it or the alternator may be failing or you may have a parasitic drain. If bad enough that can cause slow cranking but a lesser drain can make weak spark.

Have a scan tool capable of live data hooked up when it starts and look at long term fuel trim. Also check for pending OBDII codes, assuming there is no check engine light, none set yet. Check the coolant temperature sensor temperature reported.

Check fuel pressure. Clean the MAF sensor. Put in fresh gas and a bottle of fuel injector cleaner. Do these things more or less in this order, not needing to do the last if the first few solves it.

 

[wander2039]

Dealing with the same thing with our 02 Focus. Doesn't want to start when cold, when it does it's rough. But hot or at least driven within the last 8 hours fires up fine. Tried another coil no different, thought it was the crankshaft position sensor with the weird readings but that wasn't it. I did notice one or two of the plugs was wet versus two others dry. Ford's ODB really it lacking in the diagnostic department. Good luck.. I'll be watching this thread even though two different animals.

 

[The_Eric]

Try barely cracking open the throttle while cranking on a cold start.

 

[Gasbuggy]

I ordered a 5.4 E series van TB on eBay. The secret cheap performance mod for these cars. See if that improves things.

 

[mk378]

Wouldn't Ford have already put the fastest parts they stock on the police model?

You should check if the ECT sensor is telling lies.

 

[Rob_Roy]

I had a similar drivability problem with my 2001 Mercury Grand Marquis. The problem ended up being the EGR Pressure Feedback (DPFE) Sensor.

 

[HankHill]

This Vic has just over 100k on it and I've been driving it for about 4 months. The problem started after I began driving it. Any Crown Vic starts up with a nice rev then the idle comes down. Mine starts with the normal amount of cranking but fires up sluggishly right to low idle. BUT, if the engine is even slightly warm, it starts up normally the way it should. I sprayed carb cleaners all over checking for a vacuum leak. Internet research seemed to suggest the IAC was the problem. I put a brand new Delphi in (OEM supplier) and it did not change anything.

It seems to be in good tune but something may be wrong. I put new Motorcraft Platinums in soon after I started driving it, the original plugs looked good. My MPG is 20-24. Very solid for a P71 with 3.27 gears. It was never in service as a police car, it lived an easy life as a Chief's personal car. It does seem a little choked off to me though. On two separate occasions, the car had more power and was making more intake sucking noise and exhaust noise when you rolled into the throttle. Seemed to gain 30 horsepower. The first time was for a full trip, the second time, for about 5 minutes driving in the rain. I considered changing the fuel filter but it looks newer. I checked with my scanner to make sure the IAT sensor wasn't misreading and making the engine pull timing.

Not sure what to check next.

Hi Gasbuggy. I have a '10 Crown Vic P7b, with a bit less than 100k miles. Where in PA are you located? We should meet and compare cars. So about your Vic.. Your mileage is very good, I average about 17mpg combined. I have never heard any intake noise at all driving the car, ever.. Maybe the years differ with intake noise. I will agree that when you get above about 4k it turns into an animal! agreed it seems to get a burst of about, like you said, about 30 hp.
My initial thought was a cracked intake manifold, but it seems you've done your work with the carb cleaner.. I'm not sure if your year is prone to the manifold cracks, but many were. I think they fixed it in '07? Anyway try again around the manifold, and check an see if there is an intake leak. Looks like your '01 might have the update manifold with the metal coolant crossover pipe. Check and see..
I saw a guy replacing his intake runner because it was cracked where the runner met the base of the manifold, intake leak.
I replaced the plugs, fuel filter and rear diff fluid. I did a drain and fill on the trans, but I have to do it until the fluid runs clean out of the trans. I use a vacuum extractor for it.. Pan removal is blocked by a cross member.. I'm not lying on my back to fuc with that..
I wish you the best of luck and feel free to reach out and we can bulschite about or police interceptors.

 

[HankHill]

I ordered a 5.4 E series van TB on eBay. The secret cheap performance mod for these cars. See if that improves things.

Please, elaborate on this mod... Ignore my intake leak comment.. Put that bad boy on then diagnose.

 

[spasm3]

EGR not closing all the way?

 

[clinebarger]

What's the Desired RPM? The PID is RPMDES.

The desired RPM should be higher than base idle (600) even on hot start for a couple seconds, Then higher & higher the lower the engine temp is.

Have you ran a KOER Self Test? To see if it outputs a P0505 DTC (PCM cannot control engine speed).

A 2001 Ford PCM doesn't monitor the IAC Control Circuit for Opens & Shorts, I think '03 was the first year for monitored IAC Circuit.

The KOER Self Test is a important step on Ford vehicles....Especially the older ones!! During this test....The PCM will attempt to raise engine speed via the IAC.

The IAC is powered by the Powertrain Power Relay, Then the PCM pulses a ground in a PWM/Duty Cycle format to control the position of the valve.

 

[Gasbuggy]

I don't know what fixed this issue but I swapped all the coil packs and put a new Ford Racing intake manifold on it around the same time. Wasn't a problem after that.

 

[Falcon_LS]

Please, elaborate on this mod... Ignore my intake leak comment.. Put that bad boy on then diagnose.

The factory throttle body is 65 mm, the 5.4L throttle body (YC2U-BB) is 70 mm and is a direct swap for cable operated throttle bodies. You won't gain much on a stock engine, but if you have additional modifications on those years - such ported/polished heads with an 80 mm MAF/Marauder intake and tune - it will help some.

 

[FastLane]

Cracked intake manifold or gasket. Big vacumm leak.