Good Afternoon. I'm relatively new to the forum and am hoping I can get some help diagnosing an issue I am having with my 1999 Chevrolet blazer 2wd. Truck is a single owner truck with 90k. I had it exported to Europe in 2007 and drive it about 2 months out of the year while over there on vacation. Truck has been very reliable thus far. Just this past summer, I was driving it when I noticed a slightly strange feeling brake pedal, slightly squishy with a shorter travel. I immediately pulled over to see what was going on and noticed the idle was extremely rough when I pulled over. The truck was stumbling and shaking pretty violently. I shut it off, took a look around and didn't notice anything unplugged or leaking. I tried restarting it and the truck would turn over but not start unless I used full throttle. It would then start and it would be right back to stumbling and running extremely rough. The truck only starts with full throttle applied. I immediately had it towed to a nearby mechanic shop and had him check codes, etc. With it being a European shop, I'm sure he was limited in knowledge, tech and ability overall. He wasn't exactly sure what it needed so I spoke to a mechanic here in the states and he mentioned it was likely the rotor cap, plugs and wires. I ordered the OEM AcDelco parts and had them replaced while over there. No change in the truck. I was then told it may be the spider injectors, went ahead and installed that, no luck, same issue. Then went ahead and got a MAP sensor and crankshaft position sensor, replaced those without any luck. I was then able to find an individual that had an OBD scanner from the states that supposedly read the codes better. I had a plethora of codes: (P0102,P0107,P0108,P0300,P1106,P1107) These codes were collected right as I was leaving to come back to the states. At the moment, the car is in my garage and I am trying to see if anyone here would have some insight as to how to better tackle these running issues. I greatly appreciate your help with this.

Another thing to mention, he unplugged the MAF sensor at a point and the truck ran the same with no change. It is my understanding that by unplugging the MAF, there should be some change to how the vehicle runs.

Thanks in advance to anyone that chimes in.

 

Here's the trouble code diagnosis list. That's the first place to check for looking up your trouble codes.

I'm probably not the best one to help you with diagnosing the issue (that's probably George) but from your description the thing that I'd check would be the vacuum system. A broken vacuum line could be implicated in both the brake issue you first noticed, as well as the running issue. That being said, hopefully someone with more knowledge than me will chime in to help you diagnose your troubles and get your Blazer back on the road.

 

The vacuum lines can dry-rot and leak. Being a 2wd truck, there are fewer to repair and is easy to do.

Keep us posted.

 

By all means follow up on vacuum leaks. Check for intake leaks after the maf sensor. Does the idle change when you step on the brakes?

All of these codes are air flow/manifold pressure/vacuum related. When you get a code for a sensor it can be :

1. Failed sensor
2. Faulty reference voltage or conditioned ground
3. faulty signal wiring from the sensor to the ECM
4. voltage or ground problems elsewhere
5. The readings are out of bounds but correct
6. Bad ECM (very rare).

The reference voltages are not the same for the MAF (12V) and MAP (5V) sensors but I would check them anyway. Check them referenced to their conditioned grounds.

Next up are the readings themselves. In the morning when the truck is cold go to key on engine off and compare the map reading to the atmospheric pressure at your location

Next up same for the ECT reading

Warm truck, what is the MAF reading at idle and what is the reading at the moment of the full throttle 1-2 shift

All 4 fuel trim readings at idle and again at 2500 rpm

If you have misfire counters, which cylinders?

Mist the engine with water in the dark at idle and look for arcing.

Do you have recent compression readings?


There is more but this will keep us busy for now


George

 

A huge thank you to each of you on your inputs. I really appreciate the help. I am currently in the states and the car is overseas. I usually vacation there once a year in the summer. As you can imagine, once I am over there, sourcing parts, etc becomes very difficult. My goal is to gather as much information and order whatever parts I may need beforehand while I am here in the states and bring them with me and hopefully hit the ground running once I get there. I left it parked in my garage in August of 2024 and havent been there since.

What you have all mentioned makes sense in regard to vacuum leaks and failed sensors. Are there common fail points on the vacuum line system that I can look out for? I also just uploaded a video to youtube of it running, hopefully this helps a bit.
What would be the best things to purchase prior to me heading over there to ensure I have everything I may need at my disposal? I wish I can answer a lot of your questions above as to the readings, etc, however I am not near the truck at the moment.

 

It's really tough to diagnose without the vehicle available.

If you're looking for parts to take and replace when you get there, vacuum hose is cheap. Just buy a good length of it (10' is probably lots) from any parts store and cut it to length in place. I'm sure that it's been posted exact lengths and sizes on the forum in the past. It's pretty common to need to replace old dry-rotted vacuum tubes.

I guess the only other suggestion I would have is to go over the recommendations provided by George and see what you can put together from that, and make sure you have a good scan tool to access the vehicle diagnostics when you're there so that you can go through the diagnostic steps he provided.

 

Quick follow up question for you all. Thinking about this a bit more and brainstorming, could this issue be related to the brake booster failing or a vacuum leak at the brake booster?

I ask because I do remember during the rough idle, the car would really stumble badly when I press the brake pedal. Also, the whole issue started with a weird feeling brake pedal while driving.

Just wondering what your thoughts were.

 

Vacuum leaks need to be fully eliminated. The brake booster is a possible cause. One simple way to diagnose is to start pinching off lines and observe the effect. Use a fuel line clamp or vice grips with two pieces of wood. Also, watch live fuel trims, rpm and roughness when you depress the brake pedal.

George