Hard Starting and Ideals Rough

Gabe25 · #1 09-13-2005, 01:18 AM

OK, Here is the problem. I have a 94 Blazer, 4dr. 4.3 "W" motor with CMFI intake. I'm having Hard Starting when cold and Ideals rough all the time. High end she runs great. I've checked for error code and there are none. I checked for vacuum leaks. None. It feels like the engine is surging. This just starting happening all of a sudden. Less then 3K miles ago I have replaced my fuel pump, Fuel Filter, CMFI Injector Assembly, EGR Valve (Rechecked EGR for Carbon, None), Oil Pressure switch & Sensor, Temp. Switch & Sensor, Plugs (AC Delco), Cap, Rotor, Wire Set, & Ignition Coil. I was thinking if maybe it could be the Idle Air Control or Valve. Need to know your thoughts on this trouble.

wolfox · #2 09-13-2005, 02:24 AM

I would check base timing, and make sue that your EGR valve is actually working. When you swapped your fuel injector, did you also replace the fuel lines inside the plenum? Did you use an upper plenum gasket fresh out of the plastic wrap when you put it back together, or did you re-use the old one? Cleaning the IAC valve could indeed be the trick, and the simplest (read: cheapest) thing to do next. Blast it clear with throttle body cleaner and use a small, nylon bristle brush to clean it's passage. Make sure that the MAP sensor is also clear and functioning properly. When you changed plugs, did you check the gap before putting them in? Most AC/Delco plugs i got new in the box were almost all gapped way too small. Also what type of plug wires dd you use? What type/brand of cap, rotor and ignition coil did you use? Is the truck blowing black smoke at idle even when hot? Any foul odors from the exhaust, like gunpowder or burnt matches? (If you still have a working catalyst at this point, it would smell like that if running rich and/or the base timing's off) The truck utilized a base timing of 0 degrees at start - any deviation from that will make it run rough when it catches and also may show symptoms of running a little rich. Missing/poor idle may be cause by incorrect gap or non GM ignition parts. Re-used plenum gaskets can leave leaks in their wake that may also affect vehicle idle quality. And when you did all of that work, did you swap out your PCV check valve? When you experience engine loping and surging at idle, do you find yourself having to press down on the brakes really hard to get her to stop?

Gabe25 · #3 09-13-2005, 03:56 AM

Quote:

Originally Posted by wolfox

I would check base timing, and make sue that your EGR valve is actually working. When you swapped your fuel injector, did you also replace the fuel lines inside the plenum? Did you use an upper plenum gasket fresh out of the plastic wrap when you put it back together, or did you re-use the old one? Cleaning the IAC valve could indeed be the trick, and the simplest (read: cheapest) thing to do next. Blast it clear with throttle body cleaner and use a small, nylon bristle brush to clean it's passage. Make sure that the MAP sensor is also clear and functioning properly. When you changed plugs, did you check the gap before putting them in? Most AC/Delco plugs i got new in the box were almost all gapped way too small. Also what type of plug wires dd you use? What type/brand of cap, rotor and ignition coil did you use? Is the truck blowing black smoke at idle even when hot? Any foul odors from the exhaust, like gunpowder or burnt matches? (If you still have a working catalyst at this point, it would smell like that if running rich and/or the base timing's off) The truck utilized a base timing of 0 degrees at start - any deviation from that will make it run rough when it catches and also may show symptoms of running a little rich. Missing/poor idle may be cause by incorrect gap or non GM ignition parts. Re-used plenum gaskets can leave leaks in their wake that may also affect vehicle idle quality. And when you did all of that work, did you swap out your PCV check valve? When you experience engine loping and surging at idle, do you find yourself having to press down on the brakes really hard to get her to stop?

Thanks, Yes I checked the timing and its at Zero. Yes I did replace the fuel lines in the Plemum and the gasket set as well. When I changed the plug I did as always re-gap them according to the spec's. The cap and rotor are all AC Delco. I buy all my parts from Red Line Auto Parts who only carry Genuine Delco parts. There is no smoke or odor of any type coming from the exhaust. The PCV valve was just replaced 2 days ago. I tested the old one it actually was OK, But for $1.50. I thought I'd just change it anyway. When the motor does surg. Yes I do have to ride my brake alittle harder then normal. So you would say that it could be the IAC Valve. I take a look at it in the morning. Its now 10:00pm over here in Hawaii. Thanks again. I'll let you know what I find.

wolfox · #4 09-13-2005, 01:16 PM

Riding the brake harder than normal as the engine lopes and surges up and down is *classic* indication of a blocked open EGR. It's drawing more exhaust gasses than fresh air at this point, and in this state, does not develop manifold vacuum. Remove and clear the EGR valve, paying attention to the pintle. I had a chunk of carbon wedge mine open. When removed, the EGR should be shut, it's spring loaded to hold it shut. It's non-adjustable, but - gently moving the pintle with the tip of a torx bit until fully open, and then releasing it should see it shut solidly. If she doesn't, time for a new one. When it's off the front of your intake, start (if the engine catches) the engine with the valve and intake ducting removed. Be ready for a fast, high idle that races the engine, but this clears the EGR port of any remaining debris. Only do it for a few seconds, and then kill the engine. Re-install your EGR with a fresh gasket if the pintle moved freely and seals completely shut when released. If stuck open after pushing on the pintle gently, or jammed totally shut after cleaning - she's toasted. Also, do you know which MEMCAL revision you have on your truck? A later revision was released to help aid in preserving EGR health.

Gabe25 · #5 09-13-2005, 01:56 PM

I cleaned out the IAC Valve and Map Senor. There was little carbon on the plunger of the IAC. I also removed the ERG and checked it for Carbon chucks. Clean, and the plunger is closed and moves freely. Started it back up and the ideal is still rough. I'm going to take it on the freeway to see if it just needs to blow any carb cleaner out that I have used in cleaning the parts. Thanks. I'll let you know.........

Gabe25 · #6 09-13-2005, 02:26 PM

Hey Wolfox, Quick question. The Chilton book says that the IAC valve when tested with a volt Ohm meter. Pins A & B ,and C & D should read between 20 thur 30 Ohm's resistance. When I test it I get Zero resistance. Is that OK, or should there be some resistance on the valve?

wolfox · #7 09-13-2005, 02:55 PM

Zero resistance indicates a short between terminals or ground internally. Nope, that's not good. And you may have indeed found the culprit there. IAC adjusts idle dynamically to compensate for A/C, alternator loads and cold/fast idle. If the IAC went south, it can adversely affect the idle as you experience. However, I am still skeptical of having to apply more brake pressure to stop the truck. Perhaps engine output is spiking so badly with the shorted IAC that it's a rougher stop. Usually when your EGR plugs itself open, you feel almost no vacuum assist, the pedal being hard to press down when you stomp on the brakes and you get wild up and down cycles at idle too.

Gabe25 · #8 09-13-2005, 03:02 PM

Wolfox, The only time I have to press heavy on the brakes is when I'm stoped and the engine starts to surg. The high pikes causes the car to lunge forward. I'll pick up a new IAC Valve and replace it. L'll keep you posted as to how I'm doing. Thanks again for your help.
Gabe

wolfox · #9 09-13-2005, 05:46 PM

You're welcome, I just wish I thought of the possibility of an IAC valve going bad on you. *laugh*

Gabe25 · #10 09-13-2005, 06:03 PM

OK just put the new IAC valve in. Same thing High RPM runs smooth. Idealing it surging. No changes fromthe very begining. Now I'm totaly stumped. I'm open for more suggestions. I'm going to check my Fuel pressure in the line. Is there anyway in checking the popet's to see that none of them are pluged?

wolfox · #11 09-13-2005, 06:22 PM

Plugged poppets make for a miss-fire at idle, stalling under load, all sorts of strangeness. If they are plugged, they'll make the engine run lean, knock under load, or completely miss, especially at idle. It's more common for them to fail open, in which they just dump raw fuel through the engine. About the only other thing that comes to mind is start searching for any loose vacuum lines. You may have such drastic leaking of air into the intake from either a broken/missing hose anywhere between your climate controls to 4x4 vacuum switches and motors that it is making it behave this badly. Any hose that feels rough, or leaves black residue on your hands when touched needs to be replaced. They can become porous, rahter than spliting/breaking but leech more than enough air into the intake unregulated as to make for this trouble. But it has to be pretty extreme if it's making the engine bop up and down as you describe. You've got me stumped...

Gabe25 · #12 09-14-2005, 12:14 AM

Wolfox, OK, I rechecked my timming, I flooded the engine with Carb cleaner looking for a vacuum leak. all my hoses are brand new. Checked spark plug wires for proper resistance. By the way. This 1994 blazer S-10 is a Tahoe 2 wheel drive, 4 door. I don't think that would make a difference. I've notice that some of the time when I try to get parts. they are different for the LT, & ST Blazers, But Spec wise their all the same. Now that I'm totally burnt out. I'm going to just rest and attack again in the morning. I've order a new set of plugs and I'm going to take a compression test on all of the cyclinders. If you have any other idea's I'm open for all the help I can get. Thanks again.. Aloha.

wolfox · #13 09-14-2005, 12:52 AM

Just a stab in the dark at this point...

But yes, check the compression. Find if you have either a lazy valve or possibly a leaking headgasket. Though a blown gasket would do wonky things to your coolant too. Just curious, but check that too. You're not seeing any smoke or vapor after the engine's warm and at idle? Oh, and a plea to our forum moderator, Feel free to toss your hat in here any time soon BlazerLT, I am at a loss as to the common causes/fixes on this one.

s10blazerman4x4 · #14 09-14-2005, 01:18 AM

Quote:

Originally Posted by wolfox

Just a stab in the dark at this point...

But yes, check the compression. Find if you have either a lazy valve or possibly a leaking headgasket. Though a blown gasket would do wonky things to your coolant too. Just curious, but check that too. You're not seeing any smoke or vapor after the engine's warm and at idle? Oh, and a plea to our forum moderator, Feel free to toss your hat in here any time soon BlazerLT, I am at a loss as to the common causes/fixes on this one.

Did he check the oil and make sure that the coolant is not mixing in there?I agree LT needs to be here because i was thinking EGR and then IAC?What about the TPS?Throttle Position Sensor could this cause these problems?

BlazerLT · #15 09-14-2005, 12:51 PM

Remove the EGR valve again and clean out the chunk of carbon in it.

Just because you replaced it doesn't mean there is no longer any carbon in the engine that wil stick it open.

Please understand that you don't rule out ANYTHING when it comes to a problem. Just because you replaced a component doesn't mean it is perfectly fine.

ASSUME has three words.... ASS....U....ME

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