Rough idle with stiff brake but runs fine when driving normal. - S-10 Forum
 
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post #1 of 22 Old 05-12-2008, 03:26 PM Thread Starter
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Rough idle with stiff brake but runs fine when driving normal.

On a 95 4.3W CPI Blazer and today the idle was rough the rpm meter was dipping up and down 800's to 1100's and the brake petal felt stiffer. But it drives fine.

So I pulled in the bank and popped the hood and saw engine was shaking from the rough idle. I shut it off and went into my bank then when I came back out and started it up, the idle ran normal again. I drove it around for a bit and the idle is still running normal.

I know about the EPG but I have cleaned that out some time ago and check it again when I replaced the intake gasket also it didn't throw a code today either but I am wondering why my brake felt stiffer when it idle rough. I can't remember if the EPG still drive rough too but I think it did both idle and driving rough. Today only the idling was rough not the driving.

I also replaced the CPI about 3 year ago and the plugs and wires and dist. cap fuel filter etc. The fuel pump was replaced last Decemeber Recently I replace the intake manifold gasket since it was leaking.

Any idea why I experience this today? rough idle and stiff brake petal.


Thanks for inputs and replies!
Bill

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post #2 of 22 Old 05-12-2008, 04:17 PM
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Re: Rough idle with stiff brake but runs fine when driving normal.

I don't know about the rough idle, but when the idle gets messed up, the manifold vacuum will decrease, causing the reduced "power" to the power brakes, so the pedal feels stiffer.

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post #3 of 22 Old 05-12-2008, 05:18 PM
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Re: Rough idle with stiff brake but runs fine when driving normal.

Your power brakes are vacuum assisted, So there could be a few things going on.
1 Your power brake vacuum booster could be going bad....The diaphragm inside could be leaking causing lack of vacuum...stiff peddle and the air leak causing the rough idle.

2 hose leading to the vacuum booster could be split or cracked causing the stiff peddle and rough idle.

3 something else going on causing low manifold vacuum...not enough vacuum available to run the power breaks and causing the rough idle.

Last edited by lllosingit; 05-12-2008 at 05:20 PM.
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post #4 of 22 Old 05-12-2008, 05:39 PM Thread Starter
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Re: Rough idle with stiff brake but runs fine when driving normal.

Thank for the replies. The vac lines are the first thing I checked today. The one that run from upper manifold to brake booster. The line look still in a good shape and no cracking or anything like that. I also inspected all vac lines and repaced the PVC line when I replaced the intake gasket several month ago.

Also I meant to say EGR not EPG, my bad! It was the EGR that I cleaned out some years ago when it was running rough but I think it ran rough both in idle and while driving also it rhrew a code that lead me to EGR.


I am still thinking it the vac lines or loss of vac during idling but I can't pinpoint the source because it not doing this anymore. It must be a tiny leak somewhere or a tiny hole in one of the lines.

Can it be any of the vac controlled switches or valve stucked or something?


Bill

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post #5 of 22 Old 05-12-2008, 05:44 PM Thread Starter
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Re: Rough idle with stiff brake but runs fine when driving normal.

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Originally Posted by lllosingit View Post
Your power brakes are vacuum assisted, So there could be a few things going on.
1 Your power brake vacuum booster could be going bad....The diaphragm inside could be leaking causing lack of vacuum...stiff peddle and the air leak causing the rough idle.

2 hose leading to the vacuum booster could be split or cracked causing the stiff peddle and rough idle.

3 something else going on causing low manifold vacuum...not enough vacuum available to run the power breaks and causing the rough idle.

So booster going bad can have enough leak to make it idle rough? If I was to pull the vac line off the booster the engine should start to idle rough?

Any way to test the booster to determine if it going bad or not? Right now it idling fine and I haven't be able to make it idle rough again yet. I am planning on next time that it idles rough to pull the vac line off the booster and cover it with my thumb to see if it smooth it out then it pretty much the booster is at fault.


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Last edited by CBiLL; 05-12-2008 at 05:45 PM.
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post #6 of 22 Old 05-12-2008, 08:26 PM
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Re: Rough idle with stiff brake but runs fine when driving normal.

My best advice if you have the time in the near future is to go ahead and pull the EGR and clean it and also clean the exhust port that connects to it.
It only takes a tiny chunk of carbon to get stuck on the EGR plunger and release 2/3 of your vacumm.
A simple 60% test on your break vacumm line would be to pull the line at the intake and apply vacumm (be carefull not to drink break fluid in the proccess). If it hold vacumm....
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post #7 of 22 Old 05-12-2008, 08:32 PM
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Re: Rough idle with stiff brake but runs fine when driving normal.

agreed^^^


Just because you have no CEL, does not mean your egr valve is/was not held open by a piece of carbon. I am in the process of replaceing my CPI unit and It took me about 45 minutes just to clean out the carbon where the EGR valve is. It wasalmost carboned shut. This time if you remove it, buy a screened gasket. This will porevent any carbon from entering teh EGR valve.

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post #8 of 22 Old 05-12-2008, 10:43 PM Thread Starter
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Re: Rough idle with stiff brake but runs fine when driving normal.

I know about those EGR screen gasket that you can order online but I wonder if any major auto store sell them? like Autozone? something I can get locally?

Thanks
Bill
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post #9 of 22 Old 05-12-2008, 11:13 PM
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Re: Rough idle with stiff brake but runs fine when driving normal.

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I know about those EGR screen gasket that you can order online but I wonder if any major auto store sell them? like Autozone? something I can get locally?

Thanks
Bill
I doubt it. Auto Part stores amd mechanics make too much money on new EGR valves when someone hears that the ERG valve is stuck open.
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post #10 of 22 Old 05-13-2008, 08:47 PM Thread Starter
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Re: Rough idle with stiff brake but runs fine when driving normal.

Today it threw a code (Service Engine Soon light came on) then the idle smooth out.

So I went to my auto store hoping they had a OBD reader that would read a 95 Blazer because I knew it in the year between OBD I and II most folks would called it 1.5 but they didn't that that reader anymore that could read it. So they tried their newer one and it wouldn't read it which I knew it probably would not been able to read.

Years ago on a toyota van I used to jump some wires to watch dash light flashing to get the code and I wonder can that be done on the same on my 95 blazer to extract the code?


Bill
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post #11 of 22 Old 05-13-2008, 08:59 PM
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Re: Rough idle with stiff brake but runs fine when driving normal.

brake booster test.... with engine running hold the brake pedal down, if you hear a steady leaking of air, then the booster is bad. Also, the engine may try to stall or rev up. At least thats what mine is doing.

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post #12 of 22 Old 05-14-2008, 01:46 AM Thread Starter
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Re: Rough idle with stiff brake but runs fine when driving normal.

Today it idled rough again and the brake got stiff so I drove back home and left the engine running and then tried to pitch the brake booster vac hose to cut the flow and it didn't seem to change anything in the idle roughness but stepping on the brake and the engine almost wanted to die or idle went even lower and letting go the brake the idle improved so I shut it off and went to have dinner.

After dinner I went back out to see if I could pinpoint it and started the Blazer up again and it was still idling rough and I could smell a bunch of gas fume and SES came on! I was so happy to see the SES light! But funny thing is that the idle smooth out again however the SES stay on.

I knew I was going to have a hard time finding a code scanner for this 95 since it between OBD I and OBD II so I went to one auto part store and they tried a scanner and no go.

I called Autozone in hope that they have a scanner which could scan my OBD and this dude said he think his scanner can do it but he said he know how to do the paperclip trick if he couldn't pull it with his scanner so I drove over to Autozone and luckly his scanner was able to pull the code for me and clear it too.

The code he pulled was the P1406 so I went to purchase a new EGR gasket and sort of asked him if he ever heard of a gasket with screen on it and he said he have heard of it. They looked it up on the computer and it was only listing a regular standard EGR gasket but this one other worker told him to click on some other tab like aftermarket or high performance tab something like that on the EGR page and it pull up another EGR gasket .. ONE WITH THE SCREEN ON IT and they had it in stock! Last one too!! WHOO HOO it made my day!

It cost 14 dollar but I didn't care since I didn't have to order it and shipping would probably had brought it around to that price too. I was happy to get it tonight.

So this screened EGR gasket is avaiable at Autozone, at least in my town it is.

I'll be pulling EGR off tomorrow if it not raining and do a good cleaning out then put that new screen gasket in it. One thing that the gasket seem to be made out of cardboard and I am wondering if anyone know if I still put it on dry (no silicone or sealer) since the standard EGR gasket was made of metallic and it went on dry.


Thanks for all your inputs!
Bill

Last edited by CBiLL; 05-14-2008 at 01:47 AM.
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post #13 of 22 Old 05-14-2008, 10:19 AM
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Re: Rough idle with stiff brake but runs fine when driving normal.

I would put it on dry.

Sounds like you are making good progress!!

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post #14 of 22 Old 05-14-2008, 10:32 AM
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Re: Rough idle with stiff brake but runs fine when driving normal.

When you have the egr valve off, spray a good amount of carb cleanner into the intake and exhust ports that the egr connects to. Then give it a few minutes and start the engine to blow that crap out.

Don't get carb cleaner on the vacumm diaphram of the egr valve.

Good luck.
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post #15 of 22 Old 05-14-2008, 10:51 AM
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Re: Rough idle with stiff brake but runs fine when driving normal.

just a little advice, my pepboys has the screened gasket in the HELP section of parts.

maybe its the same for everyone else. i think its 10.80$ for it...

btw, your problem sounds like the EGR for sure.

John
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post #16 of 22 Old 05-14-2008, 11:30 AM Thread Starter
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Re: Rough idle with stiff brake but runs fine when driving normal.

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Originally Posted by Bill Wheats View Post
When you have the egr valve off, spray a good amount of carb cleanner into the intake and exhust ports that the egr connects to. Then give it a few minutes and start the engine to blow that crap out.

Don't get carb cleaner on the vacumm diaphram of the egr valve.

Good luck.
It an electronic controlled EGR so no vacum diaphram on this one to worry about. Also I am plan on buying seaform to use it to clean out the intake and exhaust port and the EGR.


Only thing hard about this EGR is putting it back on since it in a tight space under the upper manifold. I done it before about 4 year ago when it stuck open and it was a pain in the butt to put it back on without losing your gasket.


Bill
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post #17 of 22 Old 05-14-2008, 04:31 PM Thread Starter
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Re: Rough idle with stiff brake but runs fine when driving normal.

Took the EGR off and press the valve open then it stick staying open so I clean it up with seafoam and carb cleaner until it no longer stick staying open and spring is able to close it back.

But when I shake it the valve would start to try to open and spring would snap it back shut. A slight rattling open/close sound from the valve when shaking.

I wonder if the spring is wearing out and I should get a new one?

Bill
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post #18 of 22 Old 05-14-2008, 04:45 PM Thread Starter
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Re: Rough idle with stiff brake but runs fine when driving normal.

Geeesh 160.00 for a new EGR locally......
I think Ill chance it and put the old one back in for now.

Bill
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post #19 of 22 Old 05-14-2008, 04:53 PM
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Re: Rough idle with stiff brake but runs fine when driving normal.

The plunger should want to stay closed do to the intake vacumm sucking on it. However a small ball of carbon on the plunger or its seat on the intake will keep it from closing completely and release a large amount of intake vacumm.
If I'm right, the carbon comes mostly from not burning the fuel lean enough in the cylinders. So you probably have carbon build up in the cylinders and valve seats.
I would recommend running seafoam or some other way of removing the carbon from the rest of the system.

Good luck.
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post #20 of 22 Old 05-14-2008, 04:59 PM
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Re: Rough idle with stiff brake but runs fine when driving normal.

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Geeesh 160.00 for a new EGR locally......
I think Ill chance it and put the old one back in for now.

Bill
Mechanics got to eat steak some times too!
Can't imagine how often the shop manager tells the customer that has been out of their daily that the EGR was gunked up and the intake needs to also be cleaned, so the customer just says replace the EGR!

Look around this forum at how many people replace their fuel pumps without checking them first....
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post #21 of 22 Old 05-14-2008, 05:14 PM Thread Starter
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Re: Rough idle with stiff brake but runs fine when driving normal.

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Mechanics got to eat steak some times too!
Can't imagine how often the shop manager tells the customer that has been out of their daily that the EGR was gunked up and the intake needs to also be cleaned, so the customer just says replace the EGR!

Look around this forum at how many people replace their fuel pumps without checking them first....
They can go to Burger King ... I'll keep the steaks for myself.





Bill
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post #22 of 22 Old 05-15-2008, 06:08 PM Thread Starter
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Re: Rough idle with stiff brake but runs fine when driving normal.

I cleaned the old EGR out pretty good I think because it no longer stick open when I press it open that it quickly spring shut when I let it go.

So I went ahead reuse it putting it back in but with the screened gasket.

So far it haven't run rough idle and all looking good now.

I am having my steak cook well done tonight!


Thanks for all your replies on this!
Bill
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