2002 S10

[zr2]

Thanks for any info. in advance. I have a 2002 s10 4x4 4.3. I have been chasing around an idle problem for about a year now. I'm a student and broke so I can't just bring it in and say fix it. I did have it at the dealer and they charged me 200.00 and said sory we can't figure it out.

 

It is throwing no codes but idles down to about 300 at times other times it is perfect. Most of the time it will idle back up if you sit there a minute but coming to a stop and upon startup it will intermittantly chug down.

 

I have replaced the IAC. Plugs wires and cap are all in good shape. It blew the under hood fuse box awhile back and I ended up replaceing the vent and purge solenoid and maf sensor before I figured it out. I have checked the grounds. Has a new map sensor tps sensor pvc fuel filter fuel pressure regulator. Fuel pressure is good and the vacume is good.

 

The only other symptom is a intermittant rough idle.

 

I am about at wits end with this thing it has 185000 on ti now so anything is suspect. Oh and compression was around 145 to 150 on all cylinders.

[bill190]

Well don't go guessing and replacing anything else!

 

The way to find these problems is by testing various inputs to the engine computer. You need a GM factory service manual set for your year/model vehicle to do this testing and a multimeter. Also might need a fuel pressure gauge and in some cases an exhaust pressure gauge.

 

This is the least expensive way to fix things in the long run. This is because you can test various things as instructed to do so in the factory service manual. Then compare your test results with what it says they should be in the manual. If your test results are what they should be, then you know that component is good and does not need replacement!

 

For example there is an Engine Coolant Sensor. These cost around $25 or so. This tells the engine computer what temperature the engine is running at. Instead of just replacing this, instead you can look in the factory service manual and read about it. Learn how it works.

 

For *my* truck this sensor has different resistance readings depending on the temperature of the engine coolant. I've not driven my truck today. And it is about 80 degrees outside. So right now I will go out and "test" this sensor... Be right back...

 

...Ok, I'm back. It took 5 minutes to test my Engine Coolant Sensor. I placed my multimeter on the 20K ohms range and it read 3.0 (or 3K ohms or 3,000 ohms). Now I'll look in my factory service manual and it has a list of temperatures to ohms for this sensor. There is no listing for 80 degrees, but there is one for 77 degrees and that says it should read 2796 ohms (2.796K ohms). So my Engine Coolant Sensor is reading about what it should be.

 

For a better test, I might want to warm up the engine a bit, take a meat thermometer out of the kitchen and place it near the sensor, then see what that temperature is and test with my multimeter. If it was around 200 degrees F, that would be around 240 ohms on the sensor. To read that I would place my meter on the 2000 (or 2K) range.

 

But the good news is I don't need to replace that sensor. So I just saved $25 with 5 minutes of work! Not a bad wage if you ask me!

 

*Note the temperature sensors in other vehicles might be different and have different values for various temperatures.

[zr2]

Your right, it is a litttle stupid to just go replacing things. The thing is I thought at every turn I had put my finger on what was wrong. BTW I replaced the temp sensor and the ambiant air temp sensor also. Where can I get a goood manual? I looked at the hanes manual and decided to keep my money. I'm thinking I need either a new fuel injection setup fuel pump or computer.

 

I do have a multimeter. I just have no idea what the sensor outputs are suppost to be. Thanks for the response.

[bill190]

Basically for anything which can be repaired, the manufacturers publish "factory service manuals". Many people do not know these exist, but you can get these for small engines, refrigerators, chainsaws, vehicles, etc. You can order these from the manufacturer of the product or a dealer.

 

For GM vehicles you can order these from a GM dealer. These come in sets of 3 or 4 big books. Also here...

 

Chevrolet & Geo > 2002 > S10 Pickup/Blazer

http://www.helminc.com/helm/Result.asp?Sty...6JJ3ELB83N63TGF

 

Main page...

http://www.helminc.com

[bill190]

I'm thinking I need either a new fuel injection setup fuel pump or computer.

 

BTW - Pretty much everything on the fuel system can be tested. Follow the instructions when you get your service manuals. You would need a fuel pressure gauge for this. You will be able to determine if everything is working OK and save money by not replacing parts which are working ok. (See below)

 

As to replacing a computer, I've seen many of these needlessly replaced. People replace them because they don't understand how they work. Actually they just do what they are told! There are all sorts of "sensors" connected to this which tell it what to do.

 

For example if you severely burn your finger, then months later touch something cold and can't feel the cold, do you replace your brain? No, the problem is with the sensors in the finger not working. The brain is working just fine.

 

Well engine computers work in a similar manner. Test all the sensors to the computer FIRST before considering replacing the computer. Also the factory service manual will have tests to check the computer for proper operation.

 

What I would do next I I were you is to test the following once you get your books. These things provide input to the computer...

 

-Oxygen sensor (These should be replaced every 60,000 miles as a regular maintenance item.)

 

-Throttle position sensor (This lets the computer know the engine is at idle and this causes the IAC valve to take over idle speed control.)

 

-Coolant temperature sensor (This will tell the computer to adjust rich/lean fuel.)

 

*After* checking the above, test fuel pressure and the fuel system. Complete testing is here (along with using your factory manuals for what the test results should be)...

http://www.asashop.org/autoinc/june98/techtotech.htm

[zr2]

Thanks for the advice. That service manual is expensive, but yeah I could have paid for it twice for what i have in parts. Some of the parts I got seemed like a good idea given I have almost 200K on the truck but most of it was a waste of money.

 

I have replaced the coolant sensor and the TPS. the rear o2 sensor is new, out of the other 2 one has about 60K the other about 100K on it.

My thinking on the fuel injection is it costs 150 or more to clean it correctly or 270 shipped for the updated mpfi unit. I'm thinking just going ahead and replacing the old fuel injection concidering the miles makes since. It does have a rough idle. I have tried seafoam lucus in high concentration and techron. No luck there. The motor feels unbalanced so i am leaning twards fuel injection being the culprit.

I agree the computer is probubly not bad the only thing that makes me question that is it has been surged on. with no codes im thinking it survived.

Fuel pressure is good but my guage has not way to test volume. I will say this the pump is much quieter than it used to be. I'm not sure that is a good thing.

[Draenor]

Have you cleaned out the throttle body? Dissembled and thoroughly cleaned it?

[zr2]

Have you cleaned out the throttle body? Dissembled and thoroughly cleaned it?

 

 

I sure did. I cleaned it again yesterday. When it first started acting up it would not idle at all. I sprayed some cleaner down there to get it idleing.

 

The thing starts up then chugs down. it will get to acting right after awhile. but next key cycle it is right back to square one. its like the computer can adjust but it starts from scratch each time you key it.

 

I wander on the IAC how does the computer work that thing? Does it have a pre determined point to start making adjustments from? If it does can the computer make changes to the pre set starting point or do I have to have it tuned to set that starting point? Seems it should figure it out on its own but its not. Its like the computer suffers from memory loss.

[bill190]

I wander on the IAC how does the computer work that thing? Does it have a pre determined point to start making adjustments from? If it does can the computer make changes to the pre set starting point or do I have to have it tuned to set that starting point? Seems it should figure it out on its own but its not. Its like the computer suffers from memory loss.

 

That's what I would like to know!

 

But the car manufacturer's keep all the computer internals to themselves. There is a bit of explanation in the factory service manuals on this, but nothing technical like you would expect with anything else in this world.

 

So basically your only choice is to test all the inputs to the computer and follow the troubleshooting instructions in the service manuals. Then the flow charts, if everything else was eliminated, would lead you to replacing the computer.

 

But there is a whole lot of other stuff along the way to check.

 

If you are interested in this stuff, here is a link to an aftermarket system IAC technical page. Keep in mind this is a totally different system and has nothing to do with your vehicle!

http://www.megamanual.com/ms2/IAC.htm

[zr2]

I went ahead and got new forward o2 sensors and ordered the mpfi fuel injection from gm parts direct. o2s had more than 100K on them and I have run alot of cleaner lately, and the fuel injection is just on its way out terrible idle.

 

I hope that this will cure the thing. If it does not I'm going to break down and get a manual.

 

As soon as I can get it running right I still have to paint the thing, fix the vents, ( there coming out the top when there on floor ) and get a new radio put in.

 

Thanks again for the help and I will post back with my findings.

[zr2]

Well I went ahead and installed the mfi kit. It did not fix the problem but it does run a whole lot smoother. I went ahead and cranked in the idle set screw to compensate for it chugging down. It seems to only be idleing low once it hits closed loop then it will find the setting and generally run ok after it boggs down a couple of times.

Had it out on a camping trip last weekend and it ran good after it was warm for awhile.

 

Could a knock or crank sensor cause the problem that i'm having? I know both controll timing. It could be retarding the timing causing it to bog down at ldle?

I have not heard a hint of a knock in a long time. When it was new it would ping just a little under load like it was geting all the advance out of it that it could.