Hello

ive just got my car back from the garage ( been in since June with intermittent running issues ) they are resolved however I now have another issue with the idle when the car gets up to running temp. The revs at idle surge between 600rpm to 1200rpm ( roughly ) but is fine from cold. I unplugged the TPS and it idled better with no surging. I have ordered a new tps but when I change it do I need to position it a certain way? Thanks

 

Below s the procedure to adjust the TPS from my 1985 Corvette Factory Service Manual. You will need a Tech 1 scanner, or a voltmeter to adjust the TPS.


What other troubleshooting have you done? Are you sure the TPS is bad? Have you checked IAC valve?
Are you getting any DTC's?

 

Thanks, I have already changed the iac valve, fuel pump, fuel pressure regulator, icm, fuel injectors, fuel filter, temp sensor, maf, intake gaskets, all of the vacuum lines

I am waiting for a o2 sensor and TPS from rock auto should be here tomorrow so hopefully it fixes it this time

 

I am having the same problem on my 85. As a guess, I pulled off the vacuum line off the EGR valve and exercised the valve a few times with a hand vacuum pump. I put it all back together and started the engine. Idle was far better but after about 15 minutes of driving it started acting up a bit, now and again. I'm going to have another look in that direction shortly, with an eye on replacing the valve.

 

For both of you

First, do you have autos or manual?

Second, Have you carried out the minimum idle set procedure? you simply need a volt meter and you will be pricking the wiring to get a reading on the tps volts. you want to set an 85 to 550rpm. not 450 like was originally set by gm, and not 500 which was updated by gm later. you want to set a factory 85 to 550.

You shouldn't spend a dime on any parts until the above is known.

Third, in reality, you should be checking some other basic things like what is your base timing at , what is your fuel pressure at when running and what is fuel pressure doing when you turn key off.

Once you know this, and all is set properly, then you need to contact @Nomake Wan on the forum here, and request he burn you a hlh3200 factory gm 1985 chip. Hes done it multiple times for other 85 owners. If you have a 1985 automatic, you should all be putting the factory hlh 3200 chip in your cars. gm released an updated chip just inside 1986, for 1985's, and it makes an 85 run the same as the later cars. i've written about this a few times over the years, and it was @WVZR-1 that first suggested this was the case. every single 85 auto should do it.

My point is, that even if you have a perfectly sealed (no vac leaks) 85, it naturally runs like crap compared to the 86 and later cars. Due to the programming in the chip, from factory. If you put the HLH3200 chip in your 85 auto, you will be astonished.