Hot Start, Cold Start, and rough idle. Correlations?

[bacook]

Hi, all. my '93 4.2 is experiencing a set of symptions for which I'm trying to find correlation. Any assistance is much appreciated.

• Symptom 1: On cold start, the engine surges to 1000RPM, drops to ~200RPM and almost stalls, surges to about 1200RPM, and then evens out. This has happened to some degree since I got the truck, but recently the delta has grown so that it's closer to stalling and revving higher.
• Symptom 2: On warm start, the engine will start, but within 5 seconds die. Subsequent attempts to start will be met with, at best, a few seconds of stumbling. When it cools sufficiently symptom 2 goes away. This started about the same time as symptom 1.
• Symptom 3: Rough idle. At stop lights the whole truck rocks, and if I use light braking I can feel the engine pulsing through the drivetrain. The latter leads me to believe it's not motor mounts.

What I've done:

• I replaced the alternator with a rebuilt Magnet Marelli 100A to fix a wandering voltage problem. That did not affect any of the above symptoms.
• I replaced the temperature sensor hoping that was the problem for symptom 2. No dice because it did it again.

What have I NOT done?

• Replace wires, plugs, rotor, cap, or any fuel system stuff.
• Check that the ECU is reading the temperature sensor correctly. (I don't know how to check that)

What are your thoughts? Can the ignition wires and plugs cause all of the above symptoms? Other areas I should check? As it is, it's super reliable once started and it's been my daily driver for 1 year, 1K miles/mo. However, the hot start problem has left me stranded twice recently and I'm concerned about the symptoms deteriorating.

thanks for your advice!

 

[az_max]

[*]Replace wires, plugs, rotor, cap, or any fuel system stuff.

Start there. Replace fuel fiter, check fuel pressure (if you have the schrader valve). Clean fuel injectors. Pull the plugs and see what color they are. Replace with non platinum plugs And lastly, check voltage at the coil.

I'm betting on fuel system.

 

[Pasatiempo]

My guess is for one of the items in your intake stream. stepper motor, maf, etc. The ECU has likely reverted to a limp mode of some kind. I have a somewhat similar problem with my '96 by the way, see thread: '96 4.6 stalls after warm up.

Reading the workshop manual is a great start to trying to solve this / educate yourself to make diagnosis easier.

 

[singingcamel]

take the stepper motor out , clean of the crude and relpace, i use carb cleaner.
watch that fiber gasket thats at the base of the stepper motor.
als It might help to clean your throttle body as well. repart back.
a good tune is in order as well. rotor wires plugs as well as a dizzy cap.

 

[juanbass]

I had similar problems that left me stranded. During the no start while hot i wasn't getting any spark from the coil. I replaced the ignition control module but that didn't cure it.

Had codes for coolant and fuel temp sensors but didn't think those would fix the no spark.

Decided to replace my (less than year old) distributor under warranty and that turned out to be the fix, guess i just got a bad one. Still wasn't running proper but at least i had fire. From there I could address the sensors etc... No more stranding for now though.

FYI I am still having surge problems but i'm pretty sure they are linked to a bad alternator... my voltage regulator i believe is toast.

 

[bacook]

Thanks, all, for the input. While my wife, friends, and innocent bystanders may disagree, these trucks are worth the headache. If you can't handle an occasional change of plan, get a Toyota.
I'll start by cleaning the MAF and stepper motor, followed by plugs/wires. I cleaned the injectors last Feb when I replaced the head gaskets. I'll focus first on those things that are "free" before making financial investments into troubleshooting. I've found that with any vehicle, especially pre-OBDII, you can easily spend a mint just troubleshooting. If all goes well, I can stay one step ahead of the standard rate of decay of the many bits and pieces that make up a Rover.

 

[olmectech]

A 93 is atleast 15 years old. Get the workshop manual. Look at evey component that goes into the EFI system. There's more than 15. Start replacing the easiest and cheapest first. If it hasn't been replaced in the last 5 years, or you don't know the age, replace it.

It took me two years to relace every piece of my 93s EFI system, fuel injectors, sensors, fuel pump, fuel tank, MAF, etc. Now it runs so smooth, I can't even tell the engine is on.