Surging idle on startup

[Earnhardtfan77]

So I have been having this issue for a while now and can not figure out what's going on.. I've tried switching the maf sensor out tried switching the map sensor out and tried switching the throttle body back to the stock one with no change. I uploaded a video so you can see what is going on.any ideas. https://youtu.be/8ge0C1-xzJA

[TLewis24]

That's odd.. my guess was going to be MAF related but sounds like you tried.. does it always stop after the first few surges?

[Earnhardtfan77]

Yeah it does it a few times and then settles down.. I've searched for vacuum leaks also but couldn't seem to find any

[TheFlyingBananaSS]

Throttle or crank position sensor?

[Earnhardtfan77]

I have not tried the throttle position sensor or the crank sensor

[Jazzzed]

Does this happen if you start the engine when it is warm, or just on cold starts?

[Earnhardtfan77]

Originally Posted by Jazzzed

Does this happen if you start the engine when it is warm, or just on cold starts?

It happens on every startup..its a little more dramatic when its on a cold startup

[Jazzzed]

On one hand, its like it can't decide if it wants the cold engine high idle, or the warm engine low idle. I would consider the engine and intake temp sensors. In my mind, this has to be a sensor issue of some sort because the problem goes away. A vacuum leak or a mechanical issue would occur consistently I would think

By the way, you did address the throttle position sensor when you swapped throttle bodies.

[TheFlyingBananaSS]

Jazz may be on to something here. It sounds logical.

[Jazzzed]

Since the O2 sensors should be in open loop during startups, you can probably scratch them off the list.

I have seen other people up here who have had this problem on the V6, but it was often right after installing the 80mm throttle body. The fix seemed to always be something with the tune in those cases. So again, something throwing the computer off.

Have you disconnected your battery to reset the computer? I might try that just for kicks.

[Earnhardtfan77]

Originally Posted by Jazzzed

On one hand, its like it can't decide if it wants the cold engine high idle, or the warm engine low idle. I would consider the engine and intake temp sensors. In my mind, this has to be a sensor issue of some sort because the problem goes away. A vacuum leak or a mechanical issue would occur consistently I would think

By the way, you did address the throttle position sensor when you swapped throttle bodies.

yeah i was thinking the same thing, and its also not throwing a CEL so no help there lol..my brother has the same car as i do so im playing pick a part with his car lol...ill try the engine and intake temp sensors next and see what that does..do you think if it was the crank sensor it would throw a CEL

yeah i started the car and caused a vacuum leak and you can def. tell when there is a vacuum leak

[Earnhardtfan77]

Originally Posted by Jazzzed

Since the O2 sensors should be in open loop during startups, you can probably scratch them off the list.

I have seen other people up here who have had this problem on the V6, but it was often right after installing the 80mm throttle body. The fix seemed to always be something with the tune in those cases. So again, something throwing the computer off.

Have you disconnected your battery to reset the computer? I might try that just for kicks.

i was thinking about doing that as well, ill give that a try today also ( disconnecting the battery )

when i swapped my ported one back to the OEM one wouldnt it have corrected itself if it was the throttle body?

[Earnhardtfan77]

Thanks to jazzed I may have found my culprit. When I unplug the engine coolant temperature sensor the car starts normally. No surging. The fans come on and thinking the car is overheated but no surging. When I plugged it back in the surging returned.

When I replace the sensor should I get the OEM parts or just go to orielys or AutoZone and use what they have... Also is all my coolant going to dump out if I remove the sensor without draining the coolant first

[Jazzzed]

Originally Posted by Earnhardtfan77

Thanks to jazzed I may have found my culprit. When I unplug the engine coolant temperature sensor the car starts normally. No surging. The fans come on and thinking the car is overheated but no surging. When I plugged it back in the surging returned.

When I replace the sensor should I get the OEM parts or just go to orielys or AutoZone and use what they have... Also is all my coolant going to dump out if I remove the sensor without draining the coolant first

Nice. If it was me, the price would probably help me decide on whether to go OEM or aftermarket. I can't imagine there is much difference in the design/engineering between the two. As for whether or not the coolant makes contact with the sensor or if it is just mounted into the block, I don't know. If it does come into direct contact with the coolant though, then make sure you put some teflon tape on the threads to make sure it seals.