Good morning. I know that this topic has been posted multiple times, but I need some specific advice, so please bear with me. I bought my Blazer a few months ago, and it has had a bouncing idle. At first, when cold or randomly at idle the rpm's would dip down to about 500 and then bounce up to 1500 and then drop back down several times before leveling off again for a while. I cleaned the IAC and the EGR, and it seemed to do quite a bit better, but it would still do it pretty badly with the engine cold. After warming up, it would go away. A couple of nights ago, I pulled into a parking lot and while cruising through the lot the engine was fluctuating like crazy and almost dying. Even with giving it gas and at higher rpm's it sounded like it was missing and had an exhaust leak or something. After turning it off, I had to floor it to get it started again. The service engine light came on and threw codes 32 and 45. I replaced the EGR valve and the MAP sensor (the plastic cover had been broken off before I bought the car), and now it seems to idle a lot better (only driven it for a few hours, though). However, the next day I started it and the bouncing idle was still there and still significant. Any ideas?

I forgot to mention that when it was still surging the next morning, I replaced the IAC and when I started it back up, it was still surging as before. I haven't driven in the couple of days since then.

 

Have you tested the fuel pressure?

 

No, I haven't. Would that cause the problem when cold and then even out when warm? Are you thinking that it might be the fuel pump?

 

You seem to have checked everything else... A fuel leak inside the plenum could cause the stumble which may cause the IAC to open resulting in a surge.

 

I apologize for the delay in replying this post. I don't have a fuel pressure tester, and there is no place here that rents out tools. Does anybody have any suggestions on where to buy one? Are these $30 tools or $150 or ???

As far as what the problem might be, the car starts up immediately, but I have noticed if I haven't driven it for about a week or so, the exhaust is pretty atrocious. Also, on a daily basis, until the car has been driven for a few miles, I get kind of a white smoke out of the tail pipe. It looks kind of like moisture vapor, but heavier.

 

probably gas, leaky spider? call a shop they shouldnt charge much. but the spider assembly will!

 

Don't know if you are still having trouble, but I was having the same symptoms. Cleaned the EGR and the MAF and was moving on to the idle control when I noticed the PCV hose was just sitting on top of the connector. I pushed it on more fully, and the problem was solved. I thought I had checked over all connections in an earlier inspection, but I guess I missed that one.

 

Well, I replaced the pcv on the passenger's side of the engine, but I haven't replaced the one on the driver's side. I believe that the hose for that just goes into the air intake. If the PCV is not working correctly, could it cause this, or was it just the vacuum leak? It seems like a vacuum leak would just cause the engine to idle higher. Should I be checking for vacuum leaks that might cause this? I know that my vacuum actuator for the 4 wheel drive has a leak; could something like that affect the idle of the engine?

As far as the fuel pressure test, I took it in to a local mechanic to have them test the fuel pressure. However, in an effort to save me money (which I can't fault them for), they told me to replace the coolant temp sensor. I did, and it didn't solve the problem at all. Now I am questioning if I want to pay them $75 to do a diagnostic test when I can buy a rebuilt spider assembly for $150 from RockAuto. What are your thoughts? Should I do a diagnostic test or use that money for something else? Does anybody know how much a fuel pressure tester for the GM CPI would cost?

 

Would this pressure tester work for a '95? http://www.actron.com/product_detail.php?pid=16174

 

cant answer that. but why buy the same rebuilt problem? I would definatly go for MPFI when/if i get the chance.