Hello there!
Been experiencing some strange issues with my 98 Blazer LT 4x2. I have what seems to be an exhaust leak -- you can hear kind of a sputtering when driving, not when it's parked and idling. Have replaced the passenger side exhaust manifold -- it had some corrosion, rust and the donut gasket busted apart and left remnants inside the flange when I tried replacing that on a previous attempt. So now, I've replace the exhaust manifold on the passenger side, both side donut gaskets, flange gaskets to the cat, before and after, the catalytic converter, all 3 oxygen sensors... This previously was throwing 3 O2 sensor codes, and I thought I had it licked when I did the gaskets and O2 sensors ....until now.

However, recently, I've been noticing that when idling, the engine seems to run a bit rough. It's worse when the A/C is on, I'm in drive with the brake on, or even worse when both apply. Almost seems like the idle is too low. When driving, it seems fine, but occasionally at highway speeds, I'll get what feels like a misfire. I got a P0134 code which states that I have a slow response O2 sensor??... and the next day, I got a P1133 code. Today, I pulled the filter box off, cleaned the MAF, cleaned the throttle body, checked all connections, checked plug wires for tightness, checked all vacuum lines. Don't seem to have any issues there. I also pulled the EGR valve off, cleaned it and put it on with a new gasket. Doesn't seem to make any difference.

When I got the truck about a year ago, I replaced the injection spider, and at the same time, did a thermostat, belt, hoses, plugs, wires, cap, rotor and any number of other regular maintenance things I could think of.

I'm just confused as to what could be my problem. Any directions I should look in? Could it be the EGR tube from the driver's side to the front / top of the engine? I guess I'm just looking for anything at this point.

Please help.

Thanks,
Matt

 

Update: Today I pulled the IAC out and cleaned it, as well. Also cleaned the throttle body really good -- top, bottom and where the IAC goes in. Car seems to idle really good at about 800 RPM when first started cold, then after about 30 seconds, rough again.

I'm perplexed. Can't see replacing an EGR valve "just because." Any ideas?

 

I would just follow the vacuum lines all over to make sure that they are all good.

 

I've replaced all the ones that come off of the right side rear of the intake manifold. There's a check valve, and one goes into what looks like the fender, but I'm not sure where it goes. A few of those were pretty deteriorated and I replaced earlier. None are leaking now. Check valve works. Is there another place where I should check for vacuum leaks? It does seem like like it's something that is leaking or sticking because when I first start it, it runs perfectly fine for about the first couple minutes, then starts idling really rough. Seems like the RPM drops, too, but gradually. Idles at about 700-800, then slowly starts down to 500-400....and starts idling rough.

I did order and plan on replacing the EGR valve and gasket just on a chance it may be bad. It's pretty rough looking even after cleaning. Not convinced that that's the issue, though.

Thank you very much for your reply and if you can think of anything else, please let me know.

Matt

 

Okay, so I replaced the EGR valve...doesn't make any difference. I did notice that if I have the AC completely off, the rough idle isn't quite so bad. Drove it around a bit, and with the AC off, it seemed alright. Put the AC on, and come to a stop light, car almost wants to die. Is this indicative of anything?

 

Yesterday, I went to get gas and when checking the oil, I checked around the back to see if I could see any other vacuum lines. Checked the MAP sensor and it almost pulled right out of the upper intake manifold. The splines that hold it in are very worn out. I pushed it back in, started it back up and it seemed to idle properly, even with the AC on. Could that have been causing that much of a leak? I ordered a new MAP sensor to replace the old one.

 

Let me know what you come up with! I have a 95 that has the same symptoms and ive replaced everything but the MAP...

 

Well, I tried it today, again. Drove it around for about 10 miles, A/C on, lot of starts and stops. Seemed good. Map sensor is still on its way -- should be here later in the week. Also, I got my USB code scanner today
ScanTool 425801 OBDLink SX OBD-II Scan Tool USB Interface with OBDwiz Diagnostic Software : Amazon.com : Automotive
and have started taking some results. Want to research them a bit. May need some help interpreting the fuel trim readings.

Does anyone have any experience with this scan tool? Any tips?