Yes, but Heaton also had some 142s for as far back as I can remember, which is the early nineties. I'm reasonably sure that the 142s were still prevalent in the north east before Heaton got it's own official allocation of them.
Heaton has 33 142s allocated to it these days, so they have more 142s now than they had 143s back in the day. About half of the 26 or so Pacer diagrams at Heaton are in South Yorkshire though, I don't know whether this has always been the case.
You are a little young then
When the 143s were delivered there was no 142s at Heaton just the 1st Gen DMUs. Heaton was always self contained in the past pre-privatisation the Heaton DMUs would have only gone as far south as Darlington and Middlesborough.
The 143s had all gone for definate by the 1991, they only had about a dozen pacers then confined really to the Sunderland - MetroCentre route. Carlisle - Newcastle - Middlesborough was really in the hands of the 156.
Morpeth got a 153 as did the Middlesborough - Newcastle via Darlington route. 153s also appeared on the routes to Carlisle, Hexham and Middlesborough but no often.
Heaton had an allocation of 158s at the time as well - I think all the 3 cars.
As I said I am sure once the 156s started arriving off went the 143s and the Tyne and Wear route (whom sponsered some 143s) were replaced by the 142s