hi everyone so I just bought a 1998 blazer with a 4.3L in it, and they said when I bought it they thought it was a fuel issue because when it got warmed up the RPMs would go up and down (like 2000-1500) while driving at a steady speed and sometimes if cold enough you would have to spray starting fluid in it, and it would also stall out when driving at low speed. So I took it to have it diagnosed and the mechanic said it was the Spider injector and the MAF Sensor pigtail, I told him to do the repair, when done he told me the problem fixed most of it but they had a misfire on cylinder one and that it was the fuel injector not working so they were fixing that for free and I said great. So today I went and picked it up and he told me it ran great but yet again once it warmed up it started jumping RPMs again. So I don’t have any clue what’s wrong with it, any ideas please?

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To Rock18:
yea I’m pretty sure they switched to the multi port injection because they seemed pretty up to dat on the issue, and then the injector they did under free warranty repair because they fixed it but not completely, but I was wondering if it could be the fuel pump going out of it

Yes for starters I think you should check the fuel pressure. There is a great how to article on the site. I would think the shop should have already done this and therefore should be able to tell you their readings...

Is the check engine light on? Does the check engine light work?

I am confused about the non working fuel injector though... So we are thinking the shop installed a new, updated MPFI spider which would include a new regulator and six new fuel injectors... And one of those injectors was faulty out of the box? So, they replaced the faulty injector? Correct?

Did they use a delphi or AC Delco spider?

How old are your spark plugs? Plug wires? Cap and rotor? Are they AC Delco? These blazers are picky on what parts they like...

Honestly I’m suspicious of the work already done by the shop, but I’m suspicious of every shop!

Yea they replaced the the spider injector I’m not sure if it was an old injector or all new injectors though but I’m pretty sure they were the old injectors, but they said all around all the fuel pressures were good they gave me the numbers but I don’t have them handy, and the plugs and wires I’m not sure about either. But I’m also pretty sure they used the Delphi spider. Sorry I don’t have all this info with me I’m at work currently but do appreciate all the info.