# VG3i surges when coasting downhill at 1800 RPM



## spilsnthrils (Apr 3, 2009)

Hello and thanks to this site and all those that have posted.

I recently purchased a 1987 D21 v6 4x4 167k miles. The truck would not idle worth a crap and had a very bad surge. I hunted down all the vacuum leaks and fixed them. Check Ecc for codes showed 44. Any way from reading here I figured it was the MAF so I found a whole TBI at local junk yard for $50. I bought and cleaned the MAF from it and installed it. The truck now idles decent enough to drive but still a bit rough. I still need to go through the EGR and the rest of the electric connections and clean them. I also have an O2 sensor on the way as the tests in the ECCS level 1 showed it not functioning. 

The thing that bothers me is when I coast down hill with foot off gas and the RPMS hit exactly 1800 the motor will surge up and down about 200 RPM. As soon as I give it gas or dip below 1800 RPM or I go above 2000 RPM it will stop. This can be reproduced every time exactly at 1800 RPM. So what I am wondering is if I need to adjust the TPS or even swap it with the TPS from the other TBI. The part numbers for the MAF matched but there was a second number that is stamped on the MAF that do not match.

The surge may go away once I do the rest of the clean up. The TBI I got came off of a car that I did not regconize as it was smashed up good and missing a bunch of body parts looked like some sorta nissan wagon. The motor was a Vg3i and had Automatic Transmission as does my truck. The only real diff I saw was this motor had AC.

Thanks to any one that posts.


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## CMax03 (Jan 17, 2009)

Are you sure the hill isn't driving the engine? Drive it level @ 1800 rpm and see if it duplicates the problem!


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## 4X4D21 (Mar 9, 2009)

Im not quite sure what the problem is since you fixed all vacuum leaks, but i can tell you one thing now, the O2 sensor wont cause that beacause mine has the wires ripped out, and basically has no O2 sensor and it still runs great, just runs a bit rich


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## spilsnthrils (Apr 3, 2009)

It only surges when I coast. Does it on level road too. 

The other thing I just noticed is it wont shift into 5th gear or overdrive. I read some where that the Auto trans wont shift into overdrive if the temp is not correct. The Temp gauge shows half way on the gauge and once warm stays at the temp. I checked trany fluid and it was a little low but not below the low mark. I added some Lucus Trany slip fix as I have had good luck with that product. My mustang used to slip in first gear and the lucus trany fix fluid cleaned it right up. 

Another symptom is hard shift from first to second. Seems like the RPMS have to go to high for it to shift into second, above 3200. 3rd to 4th is fine and smooth but no 5th gear I took rpms up to 4000 and it never shifted and got 65 MPH.

I went over the vacuum lines again to double check and found no leaks. I still need to clean EGR but if I push the egr diaphram up I notice big drop in idle so it must be at least mostly closed if not closed all the way. I also followed the line that goes to the Trany and sprayed it with card cleaner and found no leaks there.

Next I'll replace the temp sensor and see if that takes care of the shifting problems. Maybe it will fix the funky surge too.

The wires where wiped out on my O2 sensor also looked like they got to close to the exhaust manifold.


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## spilsnthrils (Apr 3, 2009)

The problem was the fast idle cam was set way up. I think some one before me was messing that to get it to idle. Once I set on a cold morning to idle up to normal the surge went away when I coast so I think the throttle was bouncing on it or something or had the TPS in the wrong position.


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