Rough Running Engine

#1

I have a 1998 Chevy S-10 4-cylinder that misses and runs rough at 1500-2500 rpm. Most noticeable when ambient temperatures are below 40 degress F. Have changed everything in ignition system, engine temp sensor and crankshaft sensor. Please help.

#2

First, stop throwing parts at it. Unless the computer displayed a code pointing to those components, chances are your just wasting money. May of these sensors can be tested before replacing.

Have you determined if the fuel injectors are OK? When did you last change the fuel filter?

#3

Does “everything in the ignition system” includes spark plugs and wires? Keep going on the list of routine maintenance items: fresh air and fuel filter; pcv valve, cleaning the throttle bore and throttle plate and idle air control with Throttle Body Spray Cleaner; cleaning the MAF (Mass Air Flow) sensor with MAF cleaner.
Check all the sensors. The instructions are in the repair manual. You will need someone who knows how to use an electrical multimeter.

#4

Injectors have been checked;however, do not know when fuel filter was last changed.

#5

do not know when fuel filter was last changed.

OK then it is time to consider all maintenance items, including fuel and air filters oil and oil filter, coolant change, transmission fluid (Auto or Manual?) brake fluid change and anything else listed in the owner’s manual

While some of the above maintenance items may relate to your current issue, they all need to be done on a regular schedule to prevent problems. You don't do maintenance when there is a problem, you do it to prevent problems.  It is cheaper in the long run.  

Doing all of the past due maintenance will not only help protect your truck, it might fix it or it might make fixing it easier.
#6

Which engine temp sensor are you refering to, as there are a couple. Also in the throttle valve system there are air bypass systems, idle control circuits, some which can fail and cause rough running at specific lower rpms. You can check these with a digital multimeter

#7

Get the truck scanned for codes as a first step. AutoZone, O’Reillys, etc. will do it for free.

If the problem is not present below 1500 RPM or above 2500 then there is the possibility of an EGR system glitch.
Lower temps generally require a bit more fuel to run properly and since an EGR valve is a vacuum leak (a controlled one) maybe something is occurring in the EGR system to disrupt the air/fuel ratio.

JMHO here, but I believe that the first step in working with an engine performance problem is to always run a compression test and verify that there is not a mechanical fault with the engine. The spark plugs are usually out anyway so kill that issue right off the bat.

You would not believe how many vehicles I’ve seen over the years in which people have thrown every part in the book along with the kitchen sink in an effort to make a car run right while never considering the possibility of a cylinder(s) being down.