Rough Idle


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freddie cosme
05-01-2005, 06:09 PM
:confused: I have a 1998 Chevy Blazer with a 4.3 vortex 6 cyl. My problem is I am getting a very rough idle or stumble. I replaced plugs and wires and the problem still exist. I even went through the trouble of pulling the new plugs and check to see if I cracked one putting them in. I also cleaned the throttle body and connected my snap on MT2500 scanner. After going through the diagnostics there are no codes present. I even tapped on the MAF sensor and it does not affect the stumble at all.Any one ever have this happen to them???

blazee
05-01-2005, 06:12 PM
Did you change the cap and rotor?

blazee
05-01-2005, 06:25 PM
If you didn't replace the cap and rotor, that is probably your problem.

You can also try cleaning the EGR valve and running some Techron through the tank.

BlazerLT
05-01-2005, 06:27 PM
Replace the PCV valve also, it will cause a rough idle.

Fuel and air filter too.

freddie cosme
05-01-2005, 06:58 PM
At the risk of sounding like a total IDIOT I have to ask..... I thought this particular vehicle was distributorless?

blazee
05-01-2005, 07:05 PM
Nope, it's got one. If you replaced the wires yourself, you plugged them right in the cap. That needs to be replaced as well as the rotor inside of it. You can get an AC Delco cap and rotor from rockauto.com for a decent price. (that's where I got the ones for my 98 Blazer.)

freddie cosme
05-01-2005, 07:10 PM
I see were the plugs wire go but I thought it was the coil assembly in a DIS system..... I am an IDIOT!!!!!!!!!!! LOL

blazee
05-01-2005, 07:18 PM
I see were the plugs wire go but I thought it was the coil assembly in a DIS system..... I am an IDIOT!!!!!!!!!!! LOL

Don't feel bad a lot of people have come to this forum believing they didn't have a distributor.

The DIS is on the 2.2L S10s
Yours has EDI. (Enhanced Distributor Ignition)

freddie cosme
05-01-2005, 07:25 PM
:lol: Thanks.........Boy was I misled!!!!

blazee
05-01-2005, 07:33 PM
You're welcome.

The screws have Torq heads. You will need a T-20 for the cap and a T-15 for the rotor.

BlazerLT
05-01-2005, 10:09 PM
You're welcome.

The screws have Torq heads. You will need a T-20 for the cap and a T-15 for the rotor.

And watch you don't overtighten them or you will strip the threads out of the distributor.

They are only plastic. Tighten till firm and snug ONLY.

freddie cosme
05-05-2005, 01:40 PM
I still have the rough idle after replacing the cap and rotor rechecked to make sure i did not screw anything up and it all looks good any have any ideas??

blazee
05-05-2005, 02:11 PM
A rough idle has several common causes:

Some other routine maintenance items that can help are:

Air Filter
Fuel Filter
and PCV valve

Another common cause of a rough idle is carbon build up in the EGR valve:

Simply remove the valve, clean it, and reinstall with a new gasket.

In your other post you said you cleaned the throttle body. This may be another surprise to you...the throttle body only lets air in. You have an injector system located inside the intake manifold. It has six injectors one for each cylinder. The fuel enters the cylinder through a poppit valve. These valves are known to clog and cause a rough idle. The most effective way I know to clean them is to add a bottle of Techron to your fuel tank.

BlazerLT
05-05-2005, 04:43 PM
I still have the rough idle after replacing the cap and rotor rechecked to make sure i did not screw anything up and it all looks good any have any ideas??

What plugs are you using?

freddie cosme
05-05-2005, 11:47 PM
[QUOTE=freddie cosme]I still have the rough idle after replacing the cap and rotor rechecked to make sure i did not screw anything up and it all looks good any have any ideas??[

What do you recomend to clean the EGR?? Brakeclean??

BlazerLT
05-06-2005, 12:05 AM
TB Cleaner

freddie cosme
05-08-2005, 02:56 PM
Well replaced all that was mentioned before (major tune up) cap rotor wires pcv fuel filter air filter cleaned EGR and throttle body even added a 20 oz bottle of techron and still have a rough idle.I dont know whats next I have no codes and Im running out of patience.... Im ready to trade it in

blazer94
05-08-2005, 03:03 PM
Well replaced all that was mentioned before (major tune up) cap rotor wires pcv fuel filter air filter cleaned EGR and throttle body even added a 20 oz bottle of techron and still have a rough idle.I dont know whats next I have no codes and Im running out of patience.... Im ready to trade it in

just a thought... how were your plugs when you changed them? any glazing, burned deposits? How is your coolant level? Is it low, or is it where it should be? Any puddles under your vehicle?

freddie cosme
05-08-2005, 03:12 PM
When I removed the plugs they did not look that bad.The tip of the electrode of the plug was a little worn but I would chaulk that up to normal wear and tear. as for my coolant I have not checked it.Do you think that may cause the rough idlle? I am not running hot and I have no puddles under my car......

blazee
05-08-2005, 03:21 PM
That covers all the normal maintenance items. If the rough idle persisted, that would indicate that you may have a real problem. I would check the fuel pressure. Your local Autozone should have a fuel pressure gauge as a loaner tool. You just pay for the tool, return it within 3 days and they give your money back.

The gauge attaches to the schrader valve, it is at the back of the intake on the driver's side, it looks like a big tire valve with a black cap on it:

When you turn the key on, the pump runs for 2 seconds. While the pump is running the pressure should be 60-66psi.

When the pump primes and shuts off (engine still off) the pressure should hold steady between 55-60psi.

With the engine running the pressure should drop 3-10psi depending on engine speed due to vacuum on the regulator.

freddie cosme
05-08-2005, 03:25 PM
I have a fuel pressure guage and I will hook it up. Is it ajustable via a pressue regulator?

freddie cosme
05-08-2005, 05:29 PM
fuel pressure right on 55psi

freddie cosme
05-08-2005, 05:51 PM
:confused: Just a tidbit of info the vehicle runs good while normal driving....its when you come to a stop you feel the crappy idle.

s10blazerman4x4
05-08-2005, 06:13 PM
does it shake like a dog would when you give them a bath and they want to shake water off? Mine does that since i bought it and it seems normal because my uncle's 91 does the same.

Just my99 :2cents:

freddie cosme
05-08-2005, 06:37 PM
just a thought... how were your plugs when you changed them? any glazing, burned deposits? How is your coolant level? Is it low, or is it where it should be? Any puddles under your vehicle?
I was just curious... Why would you ask about my coolant? I was checking it out & it needs to be changed (flushed).

freddie cosme
05-08-2005, 06:44 PM
I was checking to see if I was getting any voltage to my EGR. I put my test light to the connector and I got was a weak lit test light, I checked other sensors and my test light is brightly lit. I think I may have a EGR circut problem.

blazee
05-08-2005, 07:16 PM
What was your fuel pressure for each of the following situations:

1)KEY ON, ENGINE OFF, PUMP RUNNING.

2)KEY ON, ENGINE OFF, PUMP OFF. (DOES IT REMAIN CONSTANT?)

3)KEY ON, ENGINE RUNNING.


He was probably asking about the coolant due to the notorious leaking Chevy intake gasket. Let's hope that isn't the problem. If it were leaking you should have seen deposits on the plugs and the idle would have improved briefly after changing the plugs.

I believe the EGR valve should only have voltage when it is being commanded to open and the voltage will depend on how far the ECM wants it open.

And no it isn't normal for these engines to shake like a mad dog.

After looking back over this thread, I just realized we didn't have you try cleaning the IAC valve. That would be another easy thing you could try.

freddie cosme
05-08-2005, 08:13 PM
What was your fuel pressure for each of the following situations:

1)KEY ON, ENGINE OFF, PUMP RUNNING.

2)KEY ON, ENGINE OFF, PUMP OFF. (DOES IT REMAIN CONSTANT?)

3)KEY ON, ENGINE RUNNING.


He was probably asking about the coolant due to the notorious leaking Chevy intake gasket. Let's hope that isn't the problem. If it were leaking you should have seen deposits on the plugs and the idle would have improved briefly after changing the plugs.

I believe the EGR valve should only have voltage when it is being commanded to open and the voltage will depend on how far the ECM wants it open.

And no it isn't normal for these engines to shake like a mad dog.

After looking back over this thread, I just realized we didn't have you try cleaning the IAC valve. That would be another easy thing you could try.
Key on engine off pump running 65psi
Key on engine running 57 psi
Key on engine off pump off 65psi for 2 sec and then drops to55psi

blazer94
05-08-2005, 08:34 PM
What was your fuel pressure for each of the following situations:

1)KEY ON, ENGINE OFF, PUMP RUNNING.

2)KEY ON, ENGINE OFF, PUMP OFF. (DOES IT REMAIN CONSTANT?)

3)KEY ON, ENGINE RUNNING.


He was probably asking about the coolant due to the notorious leaking Chevy intake gasket. Let's hope that isn't the problem. If it were leaking you should have seen deposits on the plugs and the idle would have improved briefly after changing the plugs.

I believe the EGR valve should only have voltage when it is being commanded to open and the voltage will depend on how far the ECM wants it open.

And no it isn't normal for these engines to shake like a mad dog.

After looking back over this thread, I just realized we didn't have you try cleaning the IAC valve. That would be another easy thing you could try.


Yes, blazee is correct, that was what I was asking about. And yes, you might have seen a brief improvement after putting in fresh plugs. plug # 6 and # 3 usually show first signs. Also, I wonder, did you try cleaning the MAF? Other common causes of missing at idle are all the things mentioned so far, plus faulty coil, bad spark plug wires ( I know you replaced them) vacumn leak, incorrect timing, faulty TPS (Throttle position Sensor) and fuel line / filter problem. Just out of curiousity, how was your oil when you changed it? does it smell of gas or coolant? blazee has you on the right track, tho, of using a system of elimination to check for cause / solution.

freddie cosme
05-08-2005, 10:56 PM
Key on engine off pump running 65psi
Key on engine running 57 psi
Key on engine off pump off 65psi for 2 sec and then drops to55psi
Im starting to wonder....My coolant resorvior is brown and my radiator is getting there. I think I will top them off and monitor them.

freddie cosme
05-08-2005, 11:54 PM
well I dont think its the intake manifold I put a pressure tester on it and it held pressure. I would think if it was an intake gasket it would leak down.

freddie cosme
05-09-2005, 01:36 PM
does anyone know how to test your injectors??

blazee
05-10-2005, 06:01 PM
Key on engine off pump running 65psi
Key on engine running 57 psi
Key on engine off pump off 65psi for 2 sec and then drops to55psi

Sorry it took so long to get back to you, for some reason this didn't show up as new in my list of subscribed threads.

Your fuel pressure is within spec so it shouldn't be an issue. I don't know how you can test the injectors yourself.

Have you tried cleaning the IAC valve, yet? After cleaning it you need to disconnect the battery for about 10 minutes so the ECM will relearn the idle. Same thing with cleaning the MAF, like blazer94 suggested.

You should also look into the things that blazer94 suggested, except the timing. The ECM controls the timing on 96 and newer models, it can't be adjusted.

blazer94
05-10-2005, 06:47 PM
Im starting to wonder....My coolant resorvior is brown and my radiator is getting there. I think I will top them off and monitor them.

I know none of us are loaded with cash, but if your coolant is rusty colored and the rad is getting that way, I would NOT top off, I would flush and fill. Bad thing about flushing tho, is sometimes if your heater core has a small leak and a rust flake is blocking it, you discover after flushing that you now have a leak in your heater core. Not too bad of a job, couple hours if you've done it before, first time can be a real bitch-kitty, tho. Also, I erred, as blazee mentioned, I forgot 95+ have ecm controlled timing. :smokin:

BlazerLT
05-12-2005, 12:13 AM
fuel pressure right on 55psi

Fuel pressure is low, should be between 61-66psi with the key on.\

Also, you should have regapped the plugs properly and not just looked at them and put them back in.

BTW, what brand of plug are you using?

freddie cosme
05-12-2005, 01:13 AM
just curious to know how many injectors does a 98 chevy blazer have?? Is it one or is it 6

blazee
05-12-2005, 06:49 AM
It has six

In your other post you said you cleaned the throttle body. This may be another surprise to you...the throttle body only lets air in. You have an injector system located inside the intake manifold. It has six injectors one for each cylinder. The fuel enters the cylinder through a poppit valve. These valves are known to clog and cause a rough idle. The most effective way I know to clean them is to add a bottle of Techron to your fuel tank.

blazee
05-12-2005, 06:59 AM
Fuel pressure is low, should be between 61-66psi with the key on.\


His fuel pressure is fine:

Key on engine off pump running 65psi
Key on engine running 57 psi
Key on engine off pump off 65psi for 2 sec and then drops to55psi

freddie cosme
05-15-2005, 10:01 PM
well folks i have done and checked everthing that was mention to me and still have a rough idle (stumble). i have used original ac delco parts. No codes present, cooling system checked and flushed.Iam leaning towards fuel injectors but I want to be sure before I swap them out. Is there any tests or diagnostic procedure that i can do to detemine if they are bad???

BlazerLT
05-15-2005, 10:13 PM
Just as a recap, can you tell us what you replaced and did?

freddie cosme
05-15-2005, 10:46 PM
Just as a recap, can you tell us what you replaced and did?
sure........cap rotor wires fuel filter air filter plugs coolant flush cleaned iac maf egr reset coputer after doing this. i scanned for codes checked my fuel pressure

BlazerLT
05-15-2005, 11:23 PM
How about a new PCV valve?

What kind of plugs did you use and what gap did you set them to?

freddie cosme
05-15-2005, 11:49 PM
How about a new PCV valve?

What kind of plugs did you use and what gap did you set them to?
yes i did change the pcv valve, as for the plugs i dont remember the number on the plug but they are whats called for that vehicle.the gap was set at .035

BlazerLT
05-16-2005, 12:00 AM
yes i did change the pcv valve, as for the plugs i dont remember the number on the plug but they are whats called for that vehicle.the gap was set at .035

What brand name did you use?

For that engine, you use:

41-932 SPARK PLUG, AC DELCO PLATINUM PLUG GAP .054

or

#12 SPARK PLUG, AC DELCO RAPIDFIRE PLUG GAP .060

0.035 is WAAAAAAY to narrow of a gap for your truck engine.

blazee
05-16-2005, 06:14 AM
Yep the plugs need to be regapped, there is a good chance they are causing your problem. You said the problem also existed before you changed plugs, hopefully with what you've done, you have fixed the original problem, too.

freddie cosme
05-16-2005, 12:03 PM
What brand name did you use?

For that engine, you use:

41-932 SPARK PLUG, AC DELCO PLATINUM PLUG GAP .054

or

#12 SPARK PLUG, AC DELCO RAPIDFIRE PLUG GAP .060

0.035 is WAAAAAAY to narrow of a gap for your truck engine.
I will pull them out and regap them..... keep your fingers crossed

BlazerLT
05-16-2005, 12:33 PM
I will pull them out and regap them..... keep your fingers crossed

Hold on there, what plugs are you using?

freddie cosme
05-16-2005, 12:47 PM
Hold on there, what plugs are you using?
41-932 is whats in the truck

BlazerLT
05-16-2005, 12:54 PM
ok, set the gap to 0.054.

Good luck.

freddie cosme
05-16-2005, 01:01 PM
ok, set the gap to 0.054.

Good luck.
I have been researching the S10 blazer This cpi unit keeps comming in to the picture.Is there any way to check this or is this a problem that pertains to early 1990's blazer? Or is this a characteristic of this vehicle regardless of the year as long as it has fuel injection??

BlazerLT
05-16-2005, 01:12 PM
I have been researching the S10 blazer This cpi unit keeps comming in to the picture.Is there any way to check this or is this a problem that pertains to early 1990's blazer? Or is this a characteristic of this vehicle regardless of the year as long as it has fuel injection??

You don't have a CPI. Don't worry about it.

freddie cosme
05-17-2005, 01:51 PM
You don't have a CPI. Don't worry about it.
Thats good to here.....but are injectors a common problem with blazers?

BlazerLT
05-17-2005, 04:53 PM
Thats good to here.....but are injectors a common problem with blazers?

Not really, we hear very few problems with the 1996+ CSFI system like what you have.

If you do have a problem, the check engine light will point you to the EXACT injector to replace.

CPI owners like me enjoy more power and torque, but we don't have the ability to diagnose an exact cylinder fuel problem.

blazee
05-17-2005, 05:29 PM
The injectors aren't the problem with the CSFI systems we have, the problem is the poppit valves. They get clogged or stick and can cause rough idle and misfires.

CSFI owners enjoy better gas mileage. :)

BlazerLT
05-17-2005, 10:20 PM
The injectors aren't the problem with the CSFI systems we have, the problem is the poppit valves. They get clogged or stick and can cause rough idle and misfires.

CSFI owners enjoy better gas mileage. :)

Ouch....... low blow. Heheeh...

BUT!.......I have more power. ;)

nahnah........

freddie cosme
05-19-2005, 01:28 PM
Well I pulled the plugs and cleaned them up and regapped them, then reinstalled them..... not much of a change. But on the flip side I FINALLY got a SES light on. it gave me a code of P00300 cylinder misfire. I went and got new ac delco wires and RECHECKED my plugs just to be sure, cleared the codes and the light came back on again P00300. The more this things stumbles and idles rough it leads me to believe I have a fuel delivery problem (fuel injectors) I have checked the coil and output to the plugs via a sparktester. what do you think? Also...with the SES light is there a way to tell what cylinder it is? Also are the poppit valves part of the injector??

BlazerLT
05-19-2005, 11:50 PM
Also recheck the cap and rotor.

A guy recently had the same problem and it turned out to be a poorly made cap and rotor.

freddie cosme
05-22-2005, 08:56 PM
:disappoin Well I have done everything that has been dicussed... the maintence needed to be done no regrets there. But the time has come to make some serious choices. Buy the ford expedition or another chevy ?

BlazerLT
05-24-2005, 06:29 PM
:disappoin Well I have done everything that has been dicussed... the maintence needed to be done no regrets there. But the time has come to make some serious choices. Buy the ford expedition or another chevy ?

How about invest $50 and some patience and get your truck fixed.

No offense, but buying a new truck because of a rough idle is wasteful.

freddie cosme
05-24-2005, 11:56 PM
How about invest $50 and some patience and get your truck fixed.

No offense, but buying a new truck because of a rough idle is wasteful.
Ok I'll bite what can I spend 50.00 bucks on to correct the problem? I have done all the maint.

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