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  #1  
Old 02-17-2012, 09:15 PM
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Default 98 blazer full tune up, still rough idle

So I have recently done a full tune up on my 98 blazer ls 4X4 135k because it was idling a bit rough and a little boggy at full throttle.

Things I have done include: plugs/wires, cap/rotor, fuel filter, cleaned throttle body/maf, put a K&N filter in it, also ran a full can of seafoam through a tank of gas.

Since doing that it seems to have gained some power while driving, but the idle is still rough. There are is no CE light on, and it's not throwing any codes. Which should be my next step? Is there an easy way to check if the injectors are bad? Also if it was a faulty egr or O2 sensor, wouldn't that trigger a CE light? Also is there a way to check if the AIC sensor is bad? I just want to know which direction I should go next to get this solved.

Any suggestions or help are greatly appreciated.
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Old 02-17-2012, 09:29 PM
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what brand ignition products did you use?
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Old 02-17-2012, 09:52 PM
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Shoot at this point I can't remember exactly. I went with the most cheap, would that make a difference?
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Old 02-17-2012, 09:53 PM
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yep these trucks prefer acdelco for ignition parts

that is possibly why its running rough
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Old 02-17-2012, 10:12 PM
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Hmm never thought of that. Think it would be worth replacing then?
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Old 02-17-2012, 10:16 PM
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Quote:
Originally Posted by quick711 View Post
Shoot at this point I can't remember exactly. I went with the most cheap, would that make a difference?
DIY 101

Actually some of those dont work right out of the box. But most of the time they last for a while. That's okay. They came with a warranty right? And you LIKE to work on your car, anyway.

The POINT is you used cheap parts and you still dont know if that SHOULD have fixed it. Whereas if you had come on here BEFORE and done some searching on the problem you wouldnt have made that mistake.

Dirty EGR will not always trigger a light. Nor will a dirty MAF.
Either or both of which could contribute to your problem. On the other hand, faulty ignition parts OFTEN trigger the light with a P0300

First step. Warm the engine, shut it off. Disconnect the MAF harness, start and see if it runs better or worse
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Old 02-18-2012, 02:28 AM
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Well as far as the cap and rotor go, I took the guy at the auto stores word for it. He was supposedly a chevy guy all the way and has only ran the cheaper ones with no issues. I had no problem paying more, but he insisted there was no reason.

All the other parts I figure needed changed anyway, or would soon.And yes I definitely do enjoy working on it. The rough idle is just annoying. I did also put premium gas in after cleaning the throttle body and MAF sensor. That may be having a negative effect as well.

I didn't think the car would run at all after disconnecting the MAF sensor. I'll have to give that a shot tomorrow. If it runs better while disconnected then I should suspect a faulty MAF I take it?

Thanks for the input.
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Old 02-18-2012, 09:40 AM
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Well as far as the cap and rotor go, I took the guy at the auto stores word for it. He was supposedly a chevy guy all the way and has only ran the cheaper ones with no issues. I had no problem paying more, but he insisted there was no reason.
Nothing personal.. but lotsa dumasses are 'experts on chebbies'.. could be he never had an engine with horizontal plug wire towers. Look closely at a classic cap, then at the 2nd gens. You'll probably get a hint at why mfg quality control matters a lot.
Quote:
All the other parts I figure needed changed anyway, or would soon.And yes I definitely do enjoy working on it. The rough idle is just annoying. I did also put premium gas in after cleaning the throttle body and MAF sensor. That may be having a negative effect as well.

I didn't think the car would run at all after disconnecting the MAF sensor. I'll have to give that a shot tomorrow. If it runs better while disconnected then I should suspect a faulty MAF I take it?

Thanks for the input.
Yes it will. Could be faulty.. or more likely dirty.
EFI programmers wisely build in redundancy for 'limp-n' purposes.

More preaching:
I cant emphasize enough that many of you who want to understand and appreciate how EFI works should beg, borrow or buy Charles Probst books on it. I havent read his books on Corvette or the Bosch-using cars but if you read his late eighties stuff on Ford EECIV {OBD1} it will give you all the basic knowledge you need on how and why all the elements work together.
Only difference between Ford and GM once they both started using MAF is GM stayed with MAP while Ford went from MAP to BAP {barometric pressure} and used a different limp-in algorithm for mixture
GM's: MAF +Air temp + coolant temp + MAP+ rpm + throttle angle

Ford's: MAF +Air temp + coolant temp + BAP+ rpm + throttle angle

If you understand the relevance of each of those sensors you understand that any one of them can be removed and the ECM can substitute a virtual reading based on what the others show.

Note: From an engineer's point of view, I prefer GM's approach for production normally aspirated engines.

Speed Density worked fine for years when you knew the displacement of the engine. Further, Ford didnt design the air pressure sensors for positive pressure more than 1 Bar {15 psi}. Since Ford had lots of experience with forced induction with their turbo 2.3 and was planning for the super coupes, they just stayed with BAP when they knew inbound air-mass.
GM of course had the Buick Turbos but evidently
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Last edited by pettyfog; 02-18-2012 at 09:59 AM.
  #9  
Old 02-20-2012, 05:30 PM
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I ended up cleaning the MAF a second time, and that did the trick. Idles like a champ. Thanks for the help guys.

Also after reading and seeing how dirty the EGR valves can get, I think I'll clean that as well. Don't think it would hurt.

Last edited by quick711; 02-20-2012 at 07:09 PM.
Old 02-20-2012, 05:30 PM
 
 
 
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1998, 98, air, blazer, body, chevy, flow, idle, idles, idling, jimmy, mass, massair, rough, sensor, shit, tune


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